no idea

[Mobilprojohnny]

hi, I'm not sure what this is next to Lincoln ear. Is on a 2003 penny.

[MintErrors]

In my opinion, It's either a stain or a clear substance, that might be removed if you choose to use a dab of pure acetone on the coin.

If you do so, it is at your own risk.

You can see through it...

[Mobilprojohnny]

I did that before i took the picture. It doesn't change.

[MintErrors]

In my opinion, there is no guarantee it would have removed it.
It might be superglue, or other clear adhesive that is just plain stuck.