Coinbuf

You will only find listings for an RPM thru 1989 including sites like Wexler's, Variety Vista or NGC Variety Plus, as starting in 1990 the mint added the mint mark to the master die.  So that coin can't be an RPM and doesn't appear to match any known DDO's for a 1994-D cent.  I would post a picture of the reverse, and look for any other signs of doubling on the coin.

I'm pretty sure that what you are seeing is a split in the copper plating around the mint mark, which is seen with some frequency on "D" mint cents of this area. The sharpness of the mint mark caused the plating to split due to the pressure of striking, exposing the underlying zinc. A repunched mintmark would not so expose the underlying zinc on the lighter punching.
   Neither doubleddie.com nor Variety Vista lists any repunched mintmarks for Lincoln cents dated after 1989. As stated in doubleddie.com, "In 1990 and 1991 the Mint began applying the mint mark for circulating coins to the master die.  After 1994 the mint mark was applied directly to the original model for all U.S. coins thus ending the RPM and OMM era." Although it would appear barely possible for a 1994-D RPM to exist, such a variety would likely have been discovered by now.

Larry  

I think it would if you just found it in a lot given the 2023 AAPLCC Collection and Attribution Standards, Third Edition under Section 2.0 "Qualifying Coins" states:
PLC must be found in a lot, driveway, lane, airport, structure or other surfaced area primarily used for parking of motor vehicles. PLC must be found and picked up by the collector at a qualifying location, or by someone with the collector at the time of discovery as long as said collector calls "dibs". PLC must as a minimum be reasonably identifiable as a known coin by shape and color. A legible date and mint mark is only required for Tier-1 PLC Resistry Sets. Placing a coin on the ground and repeatedly running over it with your monster truck does not qualify as a PLC discovery. I think that one would be an excellent candidate for an "Ulgy" class of memorial cent.  Maybe a 2010 date from the shapes and spacing?

This could be a contender for top pop for sure!

Neither, for your coin the correct term is a die crack as Greenstang noted.   A die crack is where the die has begun to break but is just a small line as it is on your coin.   If left alone and continued in use it could continue and result in a large piece of the die breaking off which could then then result in a CUD.

Fairmont, the collection that keeps on giving, and giving, and giving.

What you have is a small die crack, you can see it running up the side of the wheat stalk.  
Not really big enough to add any extra value though.

This could be a contender for top pop for sure!

For sure the founding member, but I've been taking a break for these beauties to focus on more mundane coins.  

Usually there is a test, but I'll wave that for you.  

Is membership in the AAPLCC free? And it seems I have a head start on the dimes and quarters for my registry set. 

For sure the founding member, but I've been taking a break for these beauties to focus on more mundane coins.  

@The old expert--Welcome to the NGC chat board. As indicated by @NickiO CS, your topic would best be posted on the "Newbie Coin Collecting Questions" forum, with cropped photos of both sides of the coin, where it will get more attention from other forum members.
   From your uncropped obverse photo, it appears that your circulated 1988 Lincoln cent has plating blisters, which are all too common on copper plated zinc Lincoln cents, especially those from 1982 to the early 1990s. See Plating Blisters (error-ref.com). for a detailed explanation and photos. These blisters are generally regarded by knowledgeable collectors as a quality control issue, not a mint error, and are not attributed by third-party grading services. If you enjoy collecting them, you are welcome to do so, but please do not represent to others that they are rare or have significant market value.  It doesn't "bring back the excitement of Coin Collecting for a new generation" when members of that generation are induced by sellers on certain websites to part with their hard-earned money to purchase such coins at a premium, only to find that they are unsaleable in the mainstream numismatic marketplace.
   @808maka--Welcome to you as well.  Your inquiry should have been posted as a separate topic, also on the "Newbie Coin Collecting Questions" forum, with cropped, clear photos of both sides of your coin. From what I can see, what you have is a normal 1977-D Roosevelt dime, one of 376,607,228 reported minted, which in its circulated condition is worth its face value of ten cents.

Also, I think @Coinbuf has the honor of assembling the first P-Lot collection attached, and is a founding member of AAPLCC.  

That is one tiny scale Rykel. 

+2 Contrary to what the op wrote this looks built up on the surface of the coin, glue, paint, gum, whatever.  Look at the left (viewers left) around the rim, that area is as high as the rim which would not be the case if it was an acid coin.   Then look at the steps, the gunk is higher than the steps, clearly indicating this is on the surface not eaten into the surface.

+2 Contrary to what the op wrote this looks built up on the surface of the coin, glue, paint, gum, whatever.  Look at the left (viewers left) around the rim, that area is as high as the rim which would not be the case if it was an acid coin.   Then look at the steps, the gunk is higher than the steps, clearly indicating this is on the surface not eaten into the surface.

Agree
Just something that was stuck on the coin. Doesn’t really matter what as it didn’t leave the mint looking like that

You're right, a little glob of glue or something, with the impression of whatever it was stuck to.

It looks like some type of adhesive or epoxy. Acetone or some kind of paint thinner will probably remove it. 

Looks to me like there is some sort of substance on it.    
If it was struck through, it would be concuse, yours appears raised.

1941-S Lincoln cent, scarcer "Large S" variety, NGC graded MS 66 RD (unattributed). Purchased today at a coin show.

Not an error.  Notice that the cent lettering is a mirror image. It looks like someone pressed a memorial cent up against a quarter in a vice.  So it's just damaged with no extra value.

Not to be the debbie-downer in the group, but from your photos those coins look to have some PVC damage.   I would suggest that if you have a local coin shop that you have worked with before and trust you have them look at these.   Sending coins to TPG's is expensive especially when you get details grades in return.