Justin Bieber decided to autograph Colorado with his initials. The famous graffiti artist decided it would be a good idea to write his initials in the snow -- with pee -- in Snowmass on Sunday.

According to a TMZ, and eyewitness caught the Biebs in the act in an upscale neighborhood with his pants down and "marking his territory."

Apparently his entourage of Cadillac Escalades were traveling through Snowmass when "natured" called, so the Canadian heartthrob hopped out surrounded by security guards, did his business and slid out of there.

Surprised residents inspected the area to find "JB" displayed brightly yellow in the snow (TMZ exclusive photo) -- drink some H2O Biebs.

Maybe Justin should re-think his actions since he's been in trouble with the law recently.

[TMZ]