Of the many sliding glass doors I've seen in Florida, all locked
only from the inside. Perhaps because burglars gain easy access to the inside by prying the doors upwards
--and out of the track--. (The locking mechanism is usually only a hook that can be bypassed by prying the entire door upwards with a screwdriver).
To view any identifying data, you can try the prying-upwards "workaround", with this caution: glass doors are heavy.
There are "try-keys" around. I have several rings of "try-keys" with dozens of keys on them, but they're only for certain vintage cars. Check your toolboxes, file cabinets, shed or trailer locks to see which keys "work" in the keyway. They
aren' likely to actually unlock your door; however, the brand of lock can then be determined--a good start.
