Going to note here first that I don't need examples of horizontal signals in under-freeway SPUIs, as those are common.
Normally in an SPUI with vertical signals on a centralized signal installation (a monotube or long mast arm), the left turn off-ramp signals are angled about 45 degrees to face the off ramp. But with horizontal signals, I imagine that you can't really angle it that much because of the horizontal length of the signal. Some solutions I could think of are to use shorter mast arms, with one facing the off-ramp, or not have an overhead signal at all, but I don't know how this is done in reality. Any examples of horizontal signals on over-freeway SPUIs out there?
There's one in Plano, TX at US-75 and Parker Road (https://www.google.com/maps/@33.0372704,-96.7043979,3a,75y,354.12h,83.3t/data=!3m6!1e1!3m4!1sanlRVgT7YUr8WD513e0x2A!2e0!7i16384!8i8192) (complete with Texas U-turns, of course!), and it indeed does use shorter mast arms (though I have no idea why the signal centered in the photo has its signals hung a foot below the mast arm).
Found one in Calgary between AB 8 and Macleod Trail (https://www.google.com/maps/@50.9941367,-114.0719153,3a,66.7y,58.76h,79.76t/data=!3m6!1e1!3m4!1spR2SDvChmBUU9npBCRFkbw!2e0!7i16384!8i8192). Though with this one, it seems like that the signals for both the through arterial and the off-ramps are somewhat far away from their respective stop line.