Looks like a day long project, a building sized poster is being put together on the side of the Pyramid shaped Casino in Vegas.
It could just be done as a related theme in the Movie, but I don't think there is anything more to this promotion than that, as that location isn't likely to get as much public attention as the promo spots in NY for the first one.
http://www.tfw2005.com/transformers-...-vegas-167503/

Scroll down the topic for several photos as the poster is being put together. Just don't read anything if you are avoiding spoilers.