One Of My BGS Pet Peeves...

[agentsteel53]

It would be interesting to see if Pennsylvania ever tried outline US and Pennsylvania state route shields during the relatively brief period of time when they were allowed

"relatively brief" is anything from the dawn of signage up to 1961.  A lot of the times, the "outline shield" turned out to be white with black legend anyway, so it didn't really count, but when states started using colored signage (black, green, what have you) the outline shield was the first thing defaulted to. 

and, for Penna:

[The Premier]

(click image for a full size version)

Or better yet, this:

[corco]

Well that totally nukes the uniqueness of that sign assembly 

[vdeane]

Still needs an exit tab for Fourth St too.

[LeftyJR]

PA would probably put the "South" above the I-99/US220 assembly in the second drawing.

[PAHighways]

It would be interesting to see if Pennsylvania ever tried outline US and Pennsylvania state route shields during the relatively brief period of time when they were allowed; I don't have any signing plan sheets which address this point.

The old signage for the Saw Mill Run Boulevard/Banksville Road interchange on then I-279 northbound, which was replaced in the early-mid 2000s, had outlined US and PA shields.

[PAHighways]

PA would probably put the "South" above the I-99/US220 assembly in the second drawing.

The cardinal directions are above the shields on the guides at the trumpet in Duncansville.  District 11 just eliminates the clutter by just having the Interstate on the main guide, and only mentioning the multiplexed routes to an auxiliary sign with "[route(s)] [direction] FOLLOW [Interstate] [direction]."