Personally I would try the following steps before drawing on the states resources:

1) Just use some critical thinking and ask myself "are the local criminals deciding which houses to burgle using an elaborate chalk language like a Dickensian street gang? Or would whatsapp be easier?" How does it work? Does a secondary group of thieves wander the streets at night until they happen across a chalk mark one of their scouts has left? Why would they ever risk giving the occupants prior warning?"

2) If that didn't get me there I may even google it. Let us not forget that the suggestion to call 101 is coming from within a thread where the idea of criminal chalk marks has been debunked by many commenters.

3) Speak to my friends, neighbours and family members who might A) know something about this sort of thing B) have seen who left the chalk marker C) have heard about engineering works happening on the street.

I get the desire not to discourage people from speaking to the police, i do. But I also think encouraging people to call 101 as a first port of call every time they're slightly uneasy risks a massive drain on a service that, while non emergency, still draws on police resources. After all, some people get uneasy over chalk and other urban legends.