Hi Spear,
There were a variety of different tags used on the horns over the years depending on destination, year, etc.
Normally the tags looked something like the attachment, but came in a variety of different forms.
HO=horn; FSA=automobile; 12=voltage 4=frequency. They came in pairs, like HO/FSA 12/3 and HO/FSA 12/4.
Some later tags had a lot more information on them.
Does your existing tag have any of this information?