Not all. Some sites, you have to sign up to play, some sites you just get cooler things if you sign up, and some you just don't have to sign up.
best playing games you can sign up to .com
meez is one awesome website.
you can sign up for addicting games,armor game, and y8 and y3 : ) and you can sign up for roblox
You can sign up for girlsgogames.com or club penguin!?
The pogo gaming site has some awesome, fun games and is free to sign up and play.
Grow some balls.
No sign up is necessary to play games, but you will need an account. Once you log in to the site you should be able to find several games to choose from.
You will need to sign up to EA, if you sign up with your xbox live email account, most games will automatically sign you up for the online game.
Check out lumosity.com
go to pokemonindigo
there are lot's of good sign up games! Kabillion poptropica Club penguin babydow virtual baby habbo hotel happy meal 3.0 Kidscom.com Wizard101 pandanda Hope this helps :) some sign up games are for supersecrets mostly for girls Some for boys ( i think ) weeworld and mostly for both Have fun ( it's fun for me ) pixie hollow Disney fairy zwinky cuties Garden party world Spark city whuddle world secret builders whyville