First, the only Preludes that came with the 4WS option were the Si's, made in 92 and 93.
You should have a 4WS sticker on the trunk like this:
You will also have one of these on your dash:
And last but not least, your tires will do this:
The is a sticker on the drivers door jamb that says 4WS, and the extra 4WS fuse in the underhood fuse box.
4WS only came in Brittney Blue-Green, Black, or Red.