Telescopic speed camera?

I recently saw a speed camera on the A47 hidden on a side road.

What was so wrong was that there were no signs, warnings or anything else. The camera itself was on a long pole which was raised above bushes and was facing the main road completely unseen by the traffic on the main road.

If this isn’t revenue based then what is it for?

It certainly isn’t a deterrent until after they have been caught – which seems pointless.