You could give a certain person reputation for a post you think is amusing, interesting or educational and informative for you.
If somebody asks for example in a tutorial for rep, because its something useful to you or even else that I stated above. Then this could be a reminder that you can give the reputation for his work and motivation done on this tutorial. Anyhow it's the user's decision when giving rep or not since you can not command people to give you rep after all.
What's written in a a signature and in a post is something else. First here's some facts that we probably disallow or allow:
1.) User makes a whole thread to ask/give for reputation in return as a trade (it also can be indicated as spam). - disallowed.
2.) User makes something such a tutorial, program applications etc and he included some text like "Give me reputation for making this" Then this is possible as long this person doesn't asks for rep in a new post in the same thread all the time (this also can be indicated as spam) - Allowed
3.) User asks nicely in private message for rep. (since its private) - Allowed
If you're being spammed then report it when you do. - Disallowed
4.)User ask for reputation in his own signature. - Allowed because of this sentence "its the user's decision when giving rep or not since you can not command people to give you rep after all."
Kind regards,
Xenios.