Understanding pallet ‘seals’ is an important factor and something you should mug-up on, is your own countries standards before you set out on your first collecting trip. There are many sites, which will explain these but I’m posting a few seals above to give you an example of what you are looking for.
This ‘seal’ will be located on one of the pallet blocks:
The ‘wheat stamp’ denotes IPPC compliance, confirming the pallet to be made of de-barked wood. Useful if you were unsure whether the wood was real!
DK — the country code i.e. in this case Denmark.
8C — the pallet manufacturer.
S5 — the treatment company.
HT — Heat Treated
on the second example, the British pallet, you will note that there is and additional code
DB — Debarked
All wooden crates and pallets in 74 countries of the world have an International Plant Protection Convention (IPPC) seal on them. These denote several things but the most important are the bottom two letters — you are looking for pallets with no chemical treatment. For example, in the US fumigation with methyl bromide, coded MB, is more common than in Europe, where we live, heat treatment (HT) is the norm. However, treated pallets do occur in Europe even though you will find several internet sites informing you they don’t! In the case of chemical treatment you will also see the resultant discolouration. Many garden centre suppliers, for example, dip items or conveyor spray them and their carrier pallets simultaneously and you will see immediate evidence of this in the blue-green ‘dye’ infusing the whole pallet.
The other seal above is something that is becoming more and more frequent. It’s the eco label for managed and sustainable forestry.
More information and tips on sourcing, transporting and breaking down pallets can be found on my site: https://thegreenlever.blogspot.com/p/using-repurposed-materials.html#.YOGiNbpvaV6