Bruce Schneier posts on how he signs guest registers using somebody else's name:
register, I do the same thing. I sign "Robert J. Sawyer, Toronto, ON"
– because you never know when he'll need an alibi.
This type of thing goes on all the time among friends – it is juvenile humor at its finest. But it makes me (mildly) uncomfortable to read something like this. I guess I can't understand how someone who respects privacy so much could violate someone else's so easily.
I believe the core issues of privacy revolve around loss of control and misperception. This has both.
I find it even more interesting to consider the outcome of exercises like this on a broader scale – let's say many people start doing this many times… assuming there are also many who value authenticity, it only increases the demand for a national ID program.