US flags on locomotives and cars: why?

Why do so many transit authorities put US flags on their locomotives (and often on the sides of subway cars)?

When did this start (likely after private operators ceased providing the service), and is it a requirement tied to receiving Federal dollars or something?

Thanks.

a) I recall it beginning in the flood of patriotism post-9/11.
b) Maybe someone had a surplus of flag decals.
c) Eh, why not?

I don't think it's directly tied to Federal funding, though it can't hurt.

As far as I know, for the same reason people wear them on their lapels.

it would look silly putting up foreign flags ??

mtuandrew wrote:a) I recall it beginning in the flood of patriotism post-9/11.
b) Maybe someone had a surplus of flag decals.

At NYCT it began in late 2001 (October-December). Quite a number of the IRT Redbirds (which were to be retired in the coming months) did not receive flags. New cars are delivered with the flag decals from the factory.