The protesters have been called "red shirts" for their attire, and the tag #redshirt has been used widely by Twitterers in the Bangkok area.
Here's a sample of Thai tweets about these latest events:
photo_journ (Bangkok, Thailand) #Thailand #BreakingNews #redshirt 10 trucks of military incl 2 x trucks of medics racing toward Asean Hotel now controlled by protesters qandrew (Bangkok, Thailand) Mob storms ASEAN: Thailand must have the worst riot control police in the world, either that or they are on the same side as the rioters MrRoomfinder (Thailand) Red Shirts have really disrupted the ASEAN summit!!! With so much instability, why is the Thai Baht so strong? Hmm! gnarlykitty (Bangkok, Thailand) Why attack ASEAN? In Stras & LDN they were against THOSE summits. Do most of these #redshirt even know what ASEAN is? jawntarn (Bangkok, Thailand) ขอประณามการกระทำของเสื้อแดง ที่บุกทำลายการประชุมผู้นำอาเซียน #redshirt (We decry the actions of the red shirt. The attack destroyed the ASEAN leaders meeting #Redshirt) kconsciousness (Bangkok, Thailand) my taxi driver tonight spent the whole journey sighing and assuring me that he was not a #redshirt.
Related story by Breaking Tweets:
April 9, 2009, Bangkok rallies bring city to standstill (including TwitPic)