How to recognise a shagged sheep

I get told things by my crofting neighbours and I can never be quite sure if they are pulling my leg.

However - I have been told that the sheep I see in the fields just now - with coloured bottoms - have been shagged - mated.
The ram, or tup as they call him here, has done his job.

I think it may be right.
A quick Google tells me that putting coloured paste on the underside of the tup before he mates, is called raddling.

I suppose it is quite clever really. How else would you know which sheep had been left out and still  needed attention?

 I wonder if it helps the tup - for the same reason