I went with that bracket sold on ebay for $45 and a license frame with signals built in. I like the look without the stock signals sticking out and the tag tucked up under the fender. The mirrors with built in signals came with a load compensator that took care of the flash rate.
I used the Kuruyakn lay-down number plate bracket on my bike, mounted on the rear guard. It looks like Chuckster has his fixed to the rack on the sissy-bar , hard to tell from the photo.
Tomcat's right I fixed a length of aluminium angle to the rack to mount the plate to and used a led No. plate light on the rear edge of the rack tapping into the original wires.
I then removed the original No. plate bracket and manufactured an aluminium bracket to enable the use of the original flashers, which brought them up higher.
Once you remove the original bracket you will understand what the new bracket will need to look like.
Of course it's personal choice whether you use original or after market flashers and what material you use for the brackets and where you want them to sit.
There's not much weight in the flashers so strength isn't a big issue, 2-3mm material would be sufficient, I used ally cause its easy to work.
In these pics you can see how I attached the angle to the rack and the bracket for the indicators, at least an idea and of course my new supertrapp muffler.