People scavenging through trash bins are a common sight in the hours before trash pick-up in San Francisco. They are usually on the hunt for cardboard, cans, and bottles.

But what might not be obvious is that grabbing these items from bins left on the curb for pick up is against the law.

"Even though it seems harmless, it's one of those things that does add up and costs the city money," said San Francisco Police Officer Carlos Manfredi.

While some see it as a way for poor people to generate a little income, others call it a quality of life crime.

"I have confronted people who are belligerent and I've really kind of backed off that," said Upper Noe Valley resident Christopher Faust. He says his neighborhood is being overrun by trash scavengers and the truck drivers who pay cash for stolen recyclables.

"What we're seeing now is fairly organized groups coming down the street with their bags, filling up their bags and then dumping them in the truck. Doing a street and then moving on," said Faust.

Recology, the company San Francisco pays to collect its refuse, declined to speak to us on the record. Estimates on recycling bin theft range from $5 million to $10 million, though it's impossible to tell how much actual material is stolen from blue bins.

Public Safety groups say the end result is higher garbage rates for residents. 

"Once the material is in the bin and at the curb, it's the property of Recology. So whatever money they end up losing on that, we end up paying for," said SFSAFE Public Safety Coordinator Troy Sanders.

A KTVU News crew spent two nights on San Francisco streets talking to scavengers and truck drivers. On one night, we saw a man taking cardboards and bottles from behind a Van Ness restaurant.  That business operator told us his cook was conned into opening a storage room for the man and they do not know him. That man took off after the restaurant operator came out to investigate.

In one alley one block South of City Hall, a dozen people mobbed one truck to turn in cans and bottles. Some were toting them in Recology recycling bins.

On our third stop, we caught up with a couple who was paying cash for recyclables. They told our news crew they did not speak English. But one man who turned in two bags of cans and bottles did talk to us. He was paid $16 and admits these trucks pay less but are more convenient than citywide recycling centers.

"I probably would've made double, but hey, what can you say? I need to eat tonight," he said.

Police typically cite the thieves for a public health violation -- about 15 a month. But police say they must focus on high priority crimes. There are concerns that drugs may be exchanged in some of the transactions. KTVU News crew witnessed one truck driver hand a young man a white packet which he then pops into his mouth.

"If they had some kind of illegal narcotic, it's not uncommon that they would put it in their mouth. That way, it would be easier to hide it," said Manfredi.

We tracked down one truck which bears the name J&S Recycling. That company told us they sold their vehicles four months ago and don't accept large amounts of recyclables from trucks.

Recent state legislation limits how much recyclable material can be turned in by one person. Public safety agencies say the best hope of slowing the theft is for homeowners to put their cans out in the morning before the city trucks roll up.