My favorite is the flashing yellow arrow.
http://www.dmv.de.gov/forms/driver_serv_forms/pdfs/dr_frm_manual_08182006r.pdf
Flashing Yellow Arrow
The flashing yellow arrow carries a dual meaning on Delaware roadways.
A single box signal device indicates to proceed with caution in the traffic
lane controlled by the flashing arrow. If the flashing yellow arrow is displayed
with multiple signals, it requires traffic traveling in the direction of
the flashing yellow to yield right of way. Flashing yellow with multiple signals
will change to a steady red or green arrow depending upon the intersection.
I can tell you, but then I'll have to kill you.
Seriously, though, we don't have flashing green anymore. They were removed a few years ago, because nobody understood them, even though there were signs at the intersections that had them.
A flashing green light was used at some intersections in which the
oncoming lane (to your left) had its left turns controlled by a red or flashing red arrow.
For example, if you take a look at page 53 of the manual, you'll notice that you can turn on a flashing red arrow after coming to a full stop. The manual is brain damaged, since the arrow points to the right, and of course Delaware has right turn on red anyway (unless it says otherwise). We also have left turn on red
if the turn is onto a one-way street. I had my mind blown once in Connecticut when I got pulled over for doing that, but the cop let me off when he understood that not only did I not know you couldn't do that in Connecticut, but I couldn't believe you can't do that in Connecticut. I promised not to do it again.
But, anyway... if the oncoming left turns are controlled by a light that goes from solid left arrow to flashing left arrow then, and nobody knows why, someone thought it would be a good idea if the through lane in your direction got either a solid green (when the oncoming has a solid red left arrow) or flashing green (when the oncoming has a flashing left arrow) so that you'd know when the green light is flashing that someone might be turning left in front of you.
Nobody knew what a flashing green meant, since understanding it required you to know what kind of light was on the left lane of the oncoming lane of traffic - duh. So, instead of just making it solid green, the DOT put signs up at those intersections saying something to the effect of "turns permitted on flashing green". This didn't make things any less confusing, really, since you were supposed to know they meant "turns permitted"
in the oncoming lane - some other person's turns, as if you gave a shit, really.
The former head of the DoT - Nathan Hayward III - was a world class idiot.