How can you come to Vegas and not take a picture with this iconic sign?! There's a decent amount of parking spaces here, so as long as there aren't too many people here you should be okay. The lot is easy to find and enter.
There is usually someone present to take pictures for you (for a tip). So make sure to have a tip ready if you want someone to take a picture of you and your friends! Or you can just take pictures yourselves for free.