The back is marked with what looks like a J then an arrow (not 100% sure if it's a J or V or ?) as "J ---> 10 K.T. G.F."

10 K.T. G.F = 10 karat gold filled

A site like the link below could make one suspect that watch might have value in the order of $275 maximum. Most of the watches at this site have more complications than yours. Your watch has one complication, a sweep second hand. (A complication is a feature other than an hour and minute hand.)

https://www.ebay.com/b/Girard-Perregaux-Wristwatches/31387/bn_2969425

Is there any indication that your watch has jeweled bearings? Bearings made of corundum in the final parts of the timing chain increases the life of the movement and increases value.

History and accomplishments:

https://luxwatchman.com/girard-perregaux/#girard-perregaux-history

elunia, thank you. I knew it meant it's 10 karat gold-filled, but that letter/symbol and arrow preceding it must mean something. No idea what though.

jemdandy, thank you for the links and info! I never knew that a watch feature is called a complication. I'm not sure how you tell if it has jeweled bearings, but I forwarded your info to my friend for further research. I think even $275 sounds like a lot, considering it was in a pile of junk that was getting tossed. I wonder where it came from!

ETA: new info after checking with a loupe... that mysterious letter actually looks like two 'J's that are very close together, with an arrow passing through them horizontally and pointing to the right.

Whether valuable or not, it's quite good looking. I'd look at having it cleaned and tuned up to wear or give to a family member.