Is "What is your email?" acceptable for a sign up form?
While "email address" is technically the correct term, it has become extremely common to use "email" as a shorthand for it. I can't find any online dictionaries that acknowledge this sense, but I see it used all the time, Especially in form prompts, which usually need to be terse.
There's little ambiguity, because in a phrase like "your email" it's not likely that they mean "system of exchanging messages" -- this is a concept that doesn't belong to any individual.