It was cold and late –well into a weekend night – and the police have their eye out for sex predators.
These are the men who have form, a history of abusing, molesting or taking advantage of women in Glasgow's city centre.
One is here now, right in the middle of a street buzzing with revellers leaving late-night nightclubs.
Two officers approach him, on foot, just to say hello.
Now he knows he's being watched.
"There is a small minority of men who look for women they think may be vulnerable," explains Inspector Derek Forsyth in Sauchiehall Street.
Behind him a young woman is sitting in a doorway, her bare legs on the near freezing ground and her shoes by her side. Another officer stoops to speak to her.
The girl, maybe 18, gives a thumbs-up as a friend joins her with a soft drink from a fast food joint. "She feels a bit sick," says the officer. "She has just had a bit too much to drink."
Inspector Forsyth and his colleagues don't much like talking about one of their important jobs, protecting women from the tiny handful of risky individuals who can be found in the city centre.
This, sources say, is because they don't want to spook women when, thankfully, sex offences are very rare. There hasn't been an outdoor rape in the centre of Glasgow since before last Christmas.
Police will, however, talk about what they say are increasingly good relationships with some of the major nightclubs
Val Thomson, the chief superintendent responsible for policing the city centre, said: "Clubs are very supportive around sex crime in the city, making sure their stewards are trained and can issue cards with contact numbers for women."
RePlay near Central Station is one of the city clubs that has adopted "lone women policies".
They no longer allow women who appear vulnerable – drunk – to leave the club on their own without a taxi or a friend to pick them up.
Mark Donlevy is business development manager for RePlay's owners, Stefan King's G1.
He said: "We don't allow females to leave on their own. There are people outside who try and approach such girls.
"We would rather keep intoxicated customers on our premises than have them go away.
"If we don't have a safe venue customers won't come back."
RePlay has room for more than 600 clubbers but can control who comes and goes thanks to a thumbprint electronic ID system at its door.
This is linked to clubs up and down the UK.
Anyone barred from one business on the system is barred from them all. But that doesn't protect revellers outside the club.
Neil Morrison does. The time-served steward, like his colleagues, clutches a mobile. This is for lone women leaving the club to use to call a taxi or a lift.
Mr Morrison explains: "We try to find out where her friends are or we try and find her mum and dad. If somebody wants to call someone we let them use this phone.
"Sometimes people get separated from a group or lose their phone or money. If they can't find help we ask the street pastors."
These are groups of volunteers, mostly from city churches, who are on hand with flipflops (for women whose feet have become unbearably painful in their high heels and are walking barefoot) and a bit of care for people who are the worse for wear.
They are not, stress police sources, just well-meaning do-gooders. They are properly trained and vetted.
Police know the danger spots, the dark alleyways where crimes from mugging to rape take place. Here both men and women are particularly vulnerable – not least if they are caught short.
But city centre commanders have a new tool for this too: trail bikes.
The off-road motorcycles, initially introduced to fight gangfighting in city parks, now speed up and down the back lanes of the city centre.
Stewards in another club have called the police.
A woman in her 30s had "gotten amorous" with a man she had just met on the dance floor before leaving hand in hand for the toilets with him.
She had mixed drink and cocaine.
Worried staff didn't think she was in a state to say "Yes" to anything.
As it happens the man she was with came to the same conclusion and left.
The woman ended up in hospital.
Out in the streets is Phil Braat, the convener of Strathclyde Police Authority and a city Labour councillor.
He's impressed by the good working relationships as staff call the police over vulnerable women.
"It's eye-opening," he said.