I have 2 of them, one 110 volt and the other 12 volt. Check the tag to make sure it's 110 volts. If it just says 12 or 11f (like my 12 volt horn) you'll need a 12 volt transformer to run it properly. If you're not sure take a pic of the tag. it should sound like this:
http://www.youtube.com/watch?v=sMChwc0inHA
And should be quite loud.
These are actually relabeled Benjamin horns who produced horns mainly for other manufactures, especially IBM and later Simplex when they bought out IBM's fire alarm and time clock line. I believe were produced in the 1930's as by the 40's they were redesigned and sounded like the Family Feud strike buzzer.
Looks like your horn was repainted at some point. But the good news is they require no maintenance other than an occasional test blast and are easy to fix if on the off chance something does bad or breaks.