They seem to be some sort of fruit drink from Guadalajara. The link below has a picture of a cart selling them. Do they always come with ice cream?
Just for the heck of it if anyone knows what rasas fresca are, it would be nice (also on the cart).
There's a little store near me that sells a few refreshements from Gudalejara like raspadas (the worlds best shave ice/snow cone/slushie/slurpee. They use fresh fruit puree with the shaved ice).
Anyway they sell tejuinos. The owner and I have a language barrier and I just had an embarrasing encounter with a mollete there, so I'd kind of like to know what to expect from a tejuino before ordering one.