You will either tag (single tag with just your herd no. on it) - metal as SFS says.
Or double slapmark - one on each shoulder again your herdmark
NOT both.
Again as SFS says, check with your abattoir, some only accept slapmarks, most accept both.
On transport, the pigs must be able to exit from a ramp which must be no steeper than an angle of 20 degrees, that is 36.4% to the horizontal for pigs. This will mean that you would need a particularly long ramp for a pick-up ! Also lateral protections (side gates) shall be provided so as to prevent animals from escaping. In addition to this, there are provisions on pig accomodation that a pickup is unlikely to meet. Your pigs will be too big to manually lift without breaking some other regs as well, so don't think lifting out would be an option.
Finally if you don't comply with the regs the SVS (state vet) has the power to seize (condemn) the pigs. They will still be killed, and the abattoir will still charge for that, but also charge you for subsequent dispoasl, so no meat back and lots of expense. Unlikely to happen if you have not unloaded, but if you start to get them off the back of a pickup by say pushing them, or badly lifting and one falls off a makeshift ramp with no sides, and the SVS sees this, you could well end up with this situation. Trailer is the answer - you can hire livestock trailers current rate is around £30-50, so much cheaper than buying if you only do a few a year.
Just read your other post, and if you can lift a 10 month old GOS, then there is something seriously wrong with it, so pickup definately out.