Does a platinum ring have 925 engraved on it?

Usually, platinum rings are stamped with either PLAT, PLATINUM, .950 or .900. The stamping that you're referring to normally refers to sterling silver. Unless there is a new strange alloy of platinum that I am unaware of, then the stamp you're looking at is on a piece of sterling silver jewelry.

If you're still unsure, just go to your local jeweler and ask them to test it for you. I found a good tutorial on precious metals, though, that might be helpful. You can read it by clicking on the link underneath this posting. It describes each type of precious metal in depth so you can get a better understanding of each that might allow you to determine what your ring is.