Sparton horn question

[LynnP]

I don't know diddly about anything automotive, but I got assigned the task of finding out more about this thing.

I know it's an old car horn (Model A?) and that it works. It plays a tune I don't quite recognize. A friend was interested in selling it (and who knows HOW much odd junk this guys has in his basement! He's a scavanger and collecter!). I'd like to know how to find out what a piece like this is worth. I haven't been able to dig much up in websearches because I'm not positive what exactly I'm searching for.

ETA It has four horns.