Normally it's ok. It's quite common that everybody knows that saying Secret Service we are talking about the USSS. But say it loudly:
USSS...sounds..not that good or?
Well, the USSS (

) was founded prior to the Nazi SS and as far as I remember they changed their official call sign just because of this parallel. I
can understand if people prefer USSS than SS but I never got bad feedback if the short form was used.
The USSS is quite different to other services anyway. Somehow they have the coolness others would love to have. "Special Agent" is a valid status in
the SS - and you get identity cards printed with that, ain't that cool

? For coolness, I choose the SS.
[edit on 13-10-2004 by shoo]