Oil on spark plug threads

hi all

I serviced the car and upon removing the old plugs the threads had some old oil
Deposits on them.

It didn't feel like the fresh oil i put in a week ago when I did the oil change.

The electrodes were dry as a bone just the threads.

I can't see any visible leaks on the outside of the block or from the rocket cover gasket. There's a small weap but it's nowhere near the plugs.

My car does give of a bit of blue smoke when idling at traffic lights but none when I'm driving along..

Any advice / tips welcome

Thanks 

I get it sometimes on my car and it's never seemed to be a problem, I just guest a little oil has dropped on it from some where.
I've never worried about and in the 20 years and 210,000 miles I've covered. 

If the deposit is around the threads at the top of the block, look closely at the rokker cover for a slight leak.

Or you may have spilt just a small amount of oil when topping the level up.
Only takes a small amount to run along the edge of the rokker and run down to settle around the plugs. 
When you start to unscrew them it will coat the threads. 

Just a thought!