I learned from two incidents to always cover my bike when traveling. Once while parked at a motel in a small Texas town, I awoke to find that someone had cleanly snipped off my CB antenna. Another time I was at a motel in Farmington, NM and someone let all the air out of my rear tire during the night. After the second incident I bought a travel cover. No problems since. Anything you can do to keep drunks and other jerks from fixing their eyes on your bike, the more likely they are to just move on without messing with your motorcycle.
The brand of travel cover I've always used on my bikes is one made by EZ-Touring (
Wanderer "M" model). They are very light, strong, and pack up very small so that they take up only a small amount of room in your saddlebag. A tad pricey but absolutely perfect for traveling and worth every penny: