Like the PETPET lab ray, does the regular lab ray brand your pet "ZAPPED BY LAB RAY!"?
No.
Is there any way to tell the lab ray was used?
Not really. A zapped petpet will say:
[

Zapped by the Petpet Lab Ray ]
But there isn't really a way to tell if a neopet has been zapped.
You can have an idea because some colors are only attainable through the lab, but some of them used to be atainable through fountain faerie quests.
A BD neopet heavily zapped by the lab would have relatively high HP and low defense, but not necessarily since they could be combining the lab with other training methods.
If I ZAPPED my pet and decided to throw it up for adoption, would it convert back?
No, only in some weird exceptions. Magma color pets are turned to red when pounded, and if an Ice bori is pounded, it turns blue.
Edited by Ziz, 21 August 2011 - 06:13 AM.