Can someone tell me what the firefighters emblem is called?
If you are talking about their badge, it is a shield. If not,please be more specific. 
…and welcome to Straight Dope!
It is a Malteese (sp?) Cross. Knights from Malta (Mediterranrean Island) were defengding a castle against an enemy. The enemy was using catapult launched fire-bombs. They put out fires. So do firefighters. Ergo…
Just to qualify everything, the entire post is probably bullshit after the first sentence.
There are two or three (or four) dozen fire departments on the web that have the same story, nearly word for word, to explain a relationship between the firefighter badge and the Maltese cross.
A very eleborate page is put up by San Diego Public Safety.
I tend to agree with threemae that it sounds made up. For one thing, the cross on the firefighter badge is not a Maltese cross. Looking at the crosses in the San Diego history article and comparing them to actual firefighting badges, you will see that there are a number of significant differences. Oddly, the sites located in Canada do have a Maltese cross for an emblem. I suppose that it is possible that there is some truth connecting firefighters and the Knights of St. John, but that the badge in the United States underwent a redesign at some point.