The 1990 S penny is a Proof. Normally not in circulation except for the ones from a robbery or a someone in a family spending what they shouldn't. A proof coin appears to be like a Mirror. Really, really shinny. There is no S or D or anything on a Phily Minted Penny. The others have a D for Denver and if there was an S, it would look extensively more shinning than others.

You may want to look into purchasing a Red Book by Whitman Publishing for coin information. Not necessary to purchase the latest one either. Try a used book store for one that is a few years old since the info is what you want and it doesn't change that much.

i have about 20 1990 pennys with no mark one i have is uncirculated.and another i got in my pocket change yesterday and is veryshiny and abes detail is very pronounced like the hair on his head and everything is sharply stamped.could this be one ?or just a good condition penny?

....another characteristic with a proof coin, besides the detail, is the wire like rim/edge. can you post a pic?

Here is a picture of each (proof and circulation strike). It is not my pictures, they really do look that different, at least before circulation.

and there is cleary in liberty the r is striked twice in between t and the r in photo on left.and his nose has another nose on top of his nose .but the one on right was the one i thought might be s coin but the one on the left has some flaws ithink?

one more thing abes jawline is squared off on the penny on the left were all others is streamlined?could i have 2?odd pennys by luck?

It, they could not and will not be "no "S" proof cents from 1990. It, they could not and will not be "no "S" proof cents from 1990.

Philadelphia made 6,851,765,000 of them that year and none of them had a mint mark. In fact, no cent from Philadelphia has or had a mint mark.