Paint

Paint is often a good way to get your message across and do some damage. Vehicles, billboards, and buildings are all paintable. Spray paint is one option. Splashing paint out of a container of some sort is another. Plastic soda bottles will work well there. To get more range you can put a hole in the top and screw it back on, then spray through it. Paint-bombs can be constructed by simply filling Christmas ornaments or light-bulbs with paint. Light-bulbs take some work, but are easier to come by. Cut off the bottom part of the metal, below the glass. Very carefully break out the bottom part of the glass, by the filament, inside the remaining metal ring. Fill and carefully seal. You can use a screwdriver for that. The advantage of such paint bombs is that they are surprisingly quiet. Be positive they are print-free first though. Always transport them in sealed plastic bags, in case one ruptures. Balloons can be used too, but they tend to not work as well. Paint can be inserted into soda bottles, ornaments, or bulbs using, ironically, a turkey baster. Always mix paint about 50/50 with water or paint thinner so it splatters better. Paint on glass is easy to get off, getting it on wood, metal, or stone exteriors is a lot more effective. Large markers can also work. Super-soaker type water guns filled with a paint/water mixture are effective as well. They sometimes leak and drip, so keep them in a plastic bag before and after a hit. Its impossible to wash all the paint out afterwards, making it good evidence if found, and possibly clogged after a couple uses. Bearing this in mind it may be a good idea to buy one, use it one night on a number of establishments, and dispose of it. Just remember that paint is a messy business and has a tendency to get everywhere, including all over you.
Paint stripper is another option, especially effective on vehicles. 3M Safest Strip, or Extra Strength, has the advantage of clinging to vertical surfaces. Dupli-Color makes ST-1000 Paint Stripper, available in auto parts stores. It comes in spray cans, and can eat down to bare metal in 30 minutes. Brake fluid is an effective paint stripper as well.