In Pennsylvania I'd have to say probably Old Durasig installations from the '80s, those get pretty damn ugly after a decade and a half, or even early McCain and TCT installs of the early-mid '90s, this is odd because whenever I see an even older mast-arm installation with Eagle Flatbacks from the 1970s, they look in way better condition,minus the poles, It must've been the switch from aluminum to plastic signal equipment.
Although this is more of a poor maintenance issue, the cable that carries the power conductors broke where the signal hangs from it. Picture was taken in 2013 and it's still like this today.
https://www.google.com/maps/@41.4684084,-87.3164358,3a,15y,281.72h,107.84t/data=!3m7!1e1!3m5!1saviMdx1vLRYgtqL0gMmgRA!2e0!5s20130701T000000!7i13312!8i6656!6m1!1e1?hl=en
Interestingly enough, these are the last Checker signals in NW Indiana that I know of. The one direction also supports one signal with a R-Y-G-GA combo and the light next to it is a R-Y-GA-GA combo, which in its self is rare. You can faintly see the two arrows if you look closely.
https://www.google.com/maps/@41.4685045,-87.3164673,3a,15y,200.42h,106.02t/data=!3m7!1e1!3m5!1sEBMH8mY4Ojv-iccwPTYqTQ!2e0!5s20131001T000000!7i13312!8i6656!6m1!1e1?hl=en
Unfortunately, the only link showing the arrow lit is a 2009 link, and one of the arrows was burned out.
https://www.google.com/maps/@41.4685454,-87.3163965,3a,37.5y,201.01h,89.46t/data=!3m7!1e1!3m5!1sRowdvefoMptt7ep7JMEehQ!2e0!5s20090701T000000!7i3328!8i1664!6m1!1e1?hl=en
I'm going to have to nominate the 1st Generation Durasigs on the courthouse square in downtown Athens, AL.
Extremely difficult to tell, but some of the signs for the WA-167 junction @ 24 St near Sumner aged horribly. The interchange was only built 11 years ago, but the signs make it look like the oldest junction in Seattle.
https://goo.gl/7PBafc