Building suppliers usually stock aluminium flashing of various types and I bought a 10m roll for $14. Cut into strips around 12mm wide and use an old dysfunctional biro (ballpoint pen) or borrow one off a mate to indent it with the name of the tree and other useful information.
Then roll one end around the rootstock below the graft. As the tree grows it expands the roll and I have never seen one choke the tree of blow off.
Ideal for labeling at the grafting day and after the first few grafting days now happening.
Steve Burns uses a Dremmel grinder and strips of colour bond. Mightn't be perfect for a grafting day but looks very good for the permanent job.
For the permanent planting I have a set of metal stamps from the hardware shop and I cut up aluminium similar to what is in the stop signs but get it from different sources. If your group made a few dollars at a grafting day then perhaps some thought to buying a set of metal stamps on behalf of the group to loan to members.
Neville Burley The birds love the silver ones Steve Schischka, I switched to the copper labels, they tend to leave them alone after a week as they oxidise slightly and are no longer bright. Might also add another suggestion to what Neil Barraclough put forward, keep a plan handy and document what is on each tree and where it is. Multi graft trees tend to lose one of say four at least if you know the other three your records will tell you the fourth. Anyway that's my two bob, hope it helps