Most of the time used car ads don't include the trim level of a car, and even if they do a lot of times it's wrong. Furthermore, car dealers don't seem to think electronic stability control is worth mentioning in their ads.

My question is, is there a visual cue or something I can look for in photos of an Elantra to tell is it's an ES or not? Thanks.

See if they have alloy wheels (SE) vs. hubcabps (GLS). Note, neither model says GLS or SE on the rear. If you can see the disc brake rotors through the alloy wheels, that's an SE.

Wheels are good...yeah...and lotsa se's dont have leather or moonroof...but usually they ALL come with steering wheel cruise and radio controls...

When you say ES I'm assuming you mean ESC or stability control. All SE's have them and for 07 the SE and Limited had it. When you get into the vehicle look directly below the left airvent and you will see and ESC button. Also ESC should light up on the dash. If the car doesn't have steering wheels controls and no trip computer it also doesn't have ESC, that's a GLS.