The problem with a speed sign is who is it referring to? With a limit of 60kph you could quite easily have 5 or 6 riders travelling in the pit lane at the same time!
The best idea I’ve seen so far is on iomtt thread where somebody suggested a system of flashing lights to judge your speed against. Simple cheap and quite quick to install.

I can see the reason for it having had a pit near the bottom end of pit lane a couple of years ago. Being on a stroker I needed a push, my pit crew were quite intimidated by the speed of the bikes passing them whilst they pushed me.
Although having said that I think it could cause me real problems as below 5000 the 125 will flood due to the powerjet set up and by 6500 I’m doing over 60kph. Might be pushing the bike down pit lane!

There is one last thing to think about. The statement says it will be controlled by transponder loops. Ok this works well but is entirely dependant on how many loops you have if there is just one at the start and one at the end then no problem. As it won’t matter how fast you go you will never exceed 60kph due to the amount of time your stationary re-fuelling!