Not every detention encounter with the police results in a citation. If it does result in a citation, they have preformed a non-custodial arrest. If they want to search you, they can perform a full-custody arrest even if it's for a misdemeanor that is only punishable by a fine(Atwater v. Lago Vista).

I very strongly agree with Janice Rogers Brown's opinon here: http://www.volokh.com/posts/1125942214.shtml

edit: Hmmm after reading a few things, I now think it depends on the jurisdiction whether they define receiving a citation as a non-custodial arrest.