As far as I understand it road markings have never been a requirement for any type of speed registration device. (except for the Truvelo which probably requires it's 3 little lines)
The secondary check on a Gatso can be done by measuring the difference in width of the vehicle between the two photos and some complex maths. Or something like that. Then someone realised that you could just paint lines on the road and count them instead.
Even with Vascar I believe anything can be used as a marker, a sign, a bridge, etc.
The lines on the road could have been from a fixed Gatso which had been removed (roadworks?), or from where they used to operate a portable one but now prefer using lasers (there's more chance of catching people speeding with a laser)
If the lines are very near a parking area next to the road and there is a 'large trailer sized' square box marked out in the parking area then it's an old style portable one. (I know they used to use one of these in Somerset)