Muintir na Tíre’s national co-ordinator for community alert, Liam Kelly, described the use of the so-called ‘Da Pinchi Code’ as “very disturbing”.
The chalk markings have appeared in Dublin, Drogheda, and Limerick areas in recent months.
It is understood at least eight signs are being used by the “recon unit”, one of which indicates the occupant is a vulnerable female and easily conned.
Another points to the householder being nervous and afraid, while other signs indicate the house is a good target and its owners are wealthy.
Reconnaissance units also save their burglar colleagues time by leaving signs showing there is nothing worth stealing from a house, or it is too risky to attempt burgling it.
Mr Kelly, a retired garda, said that years ago he had come across such markings, which are used regularly by criminal gangs in Britain.
“The re-emergence of these signs [in Ireland] is very disturbing,” he said.
“We advise anybody who sees them to immediately remove them and report it to the gardaí.”
He advised people in particular to keep a close eye out on the homes of elderly or vulnerable neighbours in case such markings suddenly appear outside their properties.
Mick Neary, a consultant with the firm National Security, has posted the signs on his company website to alert the public.
“My own father was a garda and he knew of the existence of these signs years ago,” he said.
“People should be especially aware of casual labourers coming to their doors looking to do work because they could be reconnaissance men.
“From our information they are also checking on the security company name on alarm boxes. They check on the internet to see if the company has gone out of business. If it went out of business a few years ago it’s likely the alarm hasn’t been serviced and the chances are it will not work properly.”
Mr Neary said the average burglar will spend just eight minutes in a house and as such could cause considerable damage in a short space of time in an estate where they know householders are out at work.
A Garda spokesman said there was “insufficient evidence to significantly link such markings with burglaries”.