Welcome to Glock Talk!
The G27 has had three different frame types, usually designated as Gen2.5, Gen3, and Gen4. Here is a photo showing the different frames, with the generations labeled; this should enable you to figure out which one you have:
The only noticeable difference between Gen2.5 and Gen3 is the fingergrooves on the frame. In the Gen2.5, the front of the fingergrooves are smooth (no checkering); in the Gen3, Glock added several rows of checkering in each fingergroove.