OK, I don't want to admit this, but...

ealandg

I can't tell the difference between a mint and a proof lincoln from 1955. How can I tell which it is?

Before you start ribbing me too hard, realize that I mainly collect pre- 1900 coins, so don't have any experience or knowledge with these things...

Placid

The label on the slab

nwcs

If it is brilliant and highly reflective, it's proof. I'm not being sarcastic. There are no PL 1955 lincolns so far as I know. If it has cartwheel luster, it's a business strike.

coppercoins

To add, if the details are sharp it's probably proof, as there are not all that many very sharp business strike 1955 cents. They way overused the dies in 1955 in Philly and most of the business strike coins ended up dull and washed out. Proofs are all sharp and have a mirror-like shine.