We have had a blue line spray painted on our front garden wall , I noticed it today (it is immediately obvious). I thought it was strange and mentioned it to DP. Next door but one neighbour has just knocked on and said she has noticed it and it has made her very uncomfortable as they were broken into a fortnight ago and she has heard of this as a tactic by criminals 'marking' properties. She wanted to let us know in case we hadn't noticed and told us she thinks we should ring 101 and tell the police. im not sure what to do about it really... I wouldn't want to waste their time and I don't know if there's anything they could actually do? WWYD?