Trolley Wire Maintenance Vehicle

Ok, being an old Philly firefighter, and retired from firefighting, I have a decent eye for detail. Looking at the Hidden City Philly site, I found this photo:
This is the second photo I have seen of a maintenance vehicle with a siren. Any ideas why? Being a red light geek, I'm pretty sure it's a Federal Model 78 dual tone, since Philly Fire was big on those in the 50s-60s.

At one time PTC (and I assume its predecessor PRT) had "emergency car houses" around the city where overhead wire crews were stationed. Think of a fire house without hoses. I know there was one near Front and Erie and another one on 13th Street at Ridge Avenue. At some point, as trolleys became less important, the sirens were removed.

As a sidebar, I once saw an article (from the 1920's?) where PRT had special "bridges" that allowed trolleys to pass over fire hoses laid across the street.

Norman

I think they were called grasshoppers, or am I thinking of something else?

Thanks, makes sense, live wires down, and not owned by PECO .

Found another one: