how do i know if my car is an s or sl

Two of the main items included in the SL are the "AM/FM/CD Changer/MP3 Audio System" and "Anti-Theft Alarm System".  There are other defining options, but these are the easiest to figure out.

Walk around to the back of the car.
Look at the right side of the trunk.
If there's an "SL" badge there, it's a SL model.
If there's no "SL" badge, it's a S.
The S also has lousy upholstery.

Both of the other posts are correct, but the EASIEST way is the wheels.  If it has alloy rims on the front (and if they do you can see the brake calibers) it is an SL.  If it has the wheel covers it is an S...  Granted you could pimp out the Versa and put some 22" rims and in that case it could be either an S or an SL...  But you would need to be brain dead to pimp out a subcompact... I own an SL and it is a great car, but when you spend 25% of the cars MSRP for new rims and tires there is something just wrong with you... Plus most people wont touch changing the rims since if you change the rims from 15" to 22" or really change the wheel size at all you need to replace the TPMS sensors or retrofit them to work in the larger rim...

ha! exactly what I was going to say! duh, right?