Safety is not a major issue on Guam. The most likely problem you'll encounter will be sunburn. Crime levels are comparable to the mainland United States, but most criminal activities relate to either domestic violence or the drug trade, so visitors usually aren't affected. Violent crime is low but property crime is high, so safeguard valuables in vehicles. Rental cars are easily identified by criminals and can be targeted. Observe caution when in the sea, as ocean currents can be strong and unpredictable. Guam is also in a major earthquake zone, and these events can and do occur every few years, but casualties are very rare.