Liberty Bell Symbols On Street Signs?

[Dandelions]

Does anyone know why some Philly street signs have the Liberty Bell symbol on them and others don't? I thought initially it may have something to do with street age, but I don't think that's it. Hmmm.....

[kf154]

I've wondered this too.

Philly 311

Why do some street signs have Liberty Bells on them?
Some street signs have a yellow liberty bell, others have a white liberty bell and some have no bell at all. What is the significance of the bell and the lack thereof?
The liberty bell symbol on our street name signs are added to make the sign bigger and more noticeable
For example, a street name sign for "SPRING GARDEN ST" is pretty large by nature of the number of letters in the name of the street.
"3rd ST" is a lot smaller, so to make the sign more visible, we add the liberty bell symbol and shift the text to make the size of the sign on par with the other signs in the City.
Modified 9/29/2009

[daninpa]

I also believe yellow means it's a dead end and white means it's a thruway, but I'm not sure.

[MarketStEl]

The various addenda on Philadelphia street signs, usually beneath the green-and-white main sign bearing the street name and house numbering coordinates:

"One way" arrows - self-explanatory.

Black text on yellow background - "NO OUTLET" - street dead-ends. Sometimes accompanied by an arrow indicating in which direction the dead end lies where a street has a full intersection with another

White text on blue background - "ARTERIAL" - usually accompanied by compass point coordinates indicating the direction(s) in which the street runs - the street is a thoroughfare

Black-and-white shields, usually accompanied by compass point coordinates - the street is a numbered state primary highway (keystone shield) or US-numbered state primary highway (US highway shield). The shields on the signs for Cottman Avenue at Roosevelt Blvd erroneously identify the street as US 73; it is PA 73. A number of signs on Broad Street similarly misidentify that street as US 611; US 611 was redesignated as a state highway more than 25 years ago. State secondary highways bear no special markers or markings, but most of the streets marked as "ARTERIAL" (above) in the city are state secondary highways (in the other 66 counties, state secondary highways are identifiable by segment-number signs at intersections)

White text on red background - the street or block in question is named in honor of a prominent figure

White Chinese characters on red background - Street is in Chinatown; the characters are the street name in (Mandarin?) Chinese.

Black Korean characters on white background - Some streets in Olney; the characters are the Korean equivalent of the street name.

Diagonal bands in the six-color rainbow - street is in the Gayborhood.

There are probably others I've missed.

[Dandelions]

Thanks! I was hoping it was something a little more symbolic, but at least I have an answer :-)