In discussions with other US glider pilots recently, and based on a
quick search of the FARs, I believe that US pilots with PPL-Glider
rating do not need any endorsements or sign-off to go cross country.
If anyone knows differently, let me know.

Before there's lots of advice to get training, fly dual x-c, etc - I
agree, and am not talking about what is the appropriate training. I
just want to verify that a PPL-G includes x-c priveledges. Of course,
clubs and rentals have their own sets of rules.