Before Garry's Mod was released on Steam, its icon was this emoticon from the Facepunch Studios and Something Awful forums:
It was probably changed to a white G on a blue background because the emoticon resembles Pac-Man, and thus they didn't want legal issues from Namco. Add
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In 2005, Garry's Mod won Mod Of The Year awards from ModDB and GameSpy which noted "It's simple, it's incredibly versatile, and it's given gamers way more hours of pleasure than all the other Counter-Strike knockoffs combined".
On the 2-year anniversary of its release on Steam (November 29, 2008) it was made known that Garry's Mod had sold over 300,000 copies at $9.99 per purchase giving it revenue of over $3,120,000 of which half goes to Valve Corporation.