Some people do ask for signs but I don't. To me asking for signs means that I don't have faith and need to receive confirmation. Either way I'm sure it's okay but I have total faith so I don't need to test the universe. :-)
Does seeing signs can be considered as manifesting your wish to receive signs?
Is it possible that one receive so many signs because one wish to receive signs so much that the universe granted his/her wish?
Is that why you shouldn't ask for a sign?