The sheriff told me that he put a warning on me, but i never sign any thing, and never got a ticket, but they?

I was in a wilderly area by San Bernardino-VictorVille area by the road where is a river me and another friend I was walking a little while in this area where suposoly is a lot prostitution and sex solicitation, and I was walking back towards the car where my friend was and the sheriff was already there, when i arrive there they where quiestioning me and kind of acuseming about me being there for solicitation the keep my expired drivers license (I was not driving at all) the never game me any ticket I never sing anypaper at all, but the sherifff guy told me that he was going to input that incident on the computer staying that if the see me again there they will arrest me, I was not doing anything just walking a long this place with my soda, I am scare about my record tell me what or how far this will afect me and what can i do. Like i said he never gave no ticket at all and never sign any paper but they keep my old driver license