How Do You Tell If It's A Proof In Circulation?

I've found a couple of proof nickels during the yearlong nickel survey that I am doing (87S,93S). If they haven't circulated for long the surfaces of the coin is a dead giveaway. Especially with the more recent issues that all have the cameo-like appearance, they stick out like a sore thumb from business strikes.

ive found tons of kennedy proofs in rolls, its easy to distinguish them because of the s mint mark that they bear. Older non s mint mark proofs are sometimes harder to determine. The strike quality is the easiest way but its not foolproof. I pulled a 1950 proof nickel out of a roll and it took me a while to realize that it was indeed a proof. Posting the image of the coin will help greatly (it did for me) as there are a multitude of people with expertises in all fields of study that regularly post on the website. Note that finding early proofs is also much more difficult merely because of there mintage numbers often in the tens of thousands rather than the millions of todays proofs that exist.

As noted already you need to purchase a thing called The Red Book by Whtiman Publishing. Usually available at most coin stores, coin shops, some hobby stores and some book stores. Not sure if still there but the Walmart web site for books used to have the lowest prices for that book. Then too you should probably acquire an album to put the coins in such as a Dansco, Whitman, etc. I would shy away from Littleton albums though.
As to proofs in change it happens all the time. Especially in high crime areas. Entire collections are stolen and just dumped into change by the robbers. Occationally some kids take their parents coins and spend them as if just normal coins. Regardless, they pop up all the time in change. Some get circulated so much they no longer look like a proof.

i found a 1951 proof penny 2 years ago in a roll.i call it a pr60.it was around until I found it.

the proof coins with have an "S" on them for the mint.

Not all S mints are proofs though, keep that in mind Joeb.

Most likely it is the business strike version.

This gets outside the realm of my expertise. If the coin is heavily worn, you would never know for sure, unless there are documented die differences.

Even if it were determined to be a heavily worn proof, I doubt it would be worth any more than a similarly worn business strike.