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Pictured in the top-right of this article is the Recycling Mobius Loop. It is found on recyclable goods and at recycling depots. This symbol is a good thing.

The 'Chasing Triangles' pictured below don't represent recycling at all. They represent the type of resin the plastic is made of. Some of it is recyclable, but some of it isn't.
In the following article we are going to look at what these symbols actually mean.
In 2001, a report was found that 8% of people understood the meaning of the symbols.

Polyethylene Terephthalate (1 - PET or PETE)
This is quite commonly found on Coke bottles. I used to think that PETE was the friendly recycling man, but this isn't so. This plastic is recyclable and is used for many different things.
PETE or PET belongs in the recycling bin in most parts of the world.

High Density Polyethylene (2 - HDPE)
Is usually used for short-life drinks such as milk. It is also used for detergent and chemical bottles.
Products marked with 2 HDPE are usually recyclable, but you should check with your collector or council to make sure.

Polyvinyl Chloride (3 PVC or V) Otherwise known as Vinyl, it is rumoured to be able to live through a nuclear holocaust.
It is used for a types of packaging, bondage suits, and jackets owned by 1970's detectives. When recycled it can be used for many household fittings, as well as speed-bumps.
Most Councils don't recycle this.

Low Density Polyethylene (4 LDPE)
It is widely used in wire and cable. It is also found in carpet. You might find the LDPE triangle label on squeezy bottles and frozen food bags.
When recycled it can be be turned into compost bins and bin liners.
Sometimes recycled, check with council.

Polypropylene (5 PP)
Polypropylene is strong and is resistant to chemicals. It has a high melting-point and can be used on the inside of a thermos.
You will see the 5 PP triangle on medicine bottles.
It can be re-incarnated as bicycle racks, rakes and packing pallets.
Sometimes recycled, check with council.

Polystyrene (6 PS)
Polystyrene can be formed into rigid products, as well as foamy. It can also be known as Styrofoam, and was immortalized in song when Denis Leary rants about it in Asshole , paying tribute to its non-biodegrading properties.
Sometimes recycled, check with council.

OTHER (7 Other)
This is for plastics of no specific number, or for plastics made up of a number of different resins.
It can be found on certain food product bottles, and recycled into custom-made products.
Rarely recycled, check with council.

Acrylonitrile Butadiene Styrene (ABS)
This originally wasn't part of resin identification system (that is why it doesn't get a number). Its components contain likely human carcinogens, but as a whole it isn't known to be harmful.
Rarely recycled, check with council.

If I havent' addressed this enough, contact your local Council or Recycling Agent to find out what plastics are recyclable.
The Plymouth City Council UK (where I reside) told me that the triangles are disregarded at the point where the items are sorted for recycling. It is simply not practicle for workers to check for a tiny, sometimes invisible, triangle.
They also ask that you take the cap off the plastic bottles.
Everywhere in the world is different, with different standards. So it is best to check with yours.
But know this, the triangle doesn't neccessarily mean it is recyclable. Occasionally you will find a triangle with an 'R' before the code. For example, RPET. That means it has been made from recycled plastic.

Interesting Point. The Recycling Mobius Loop was modelled on the Mobius Strip...

The Mobius Strip is the trippiest little thing ever.

It was named after the astronomer and mathematician August Ferdinand Möbius. In 1858, he realised that you can make a loop one-sided by putting a half turn in it. It sounds impossible but it isn't. Check out this link to learn how to make one and mess with the minds of your children.

Incidentally, fellow mathematician Johann Benedict Listing devised the same object in July 1858. But he didn't get in quick enough, much like Alfred Russell Wallace, who was gazzumped by Charles Darwin to fame, hatred, ridicule and immortality (also in 1858).