Recent email to seller: 

Please note that if the sign has no firm backing, two pieces of wood will be required.

Hi there

that's great. I can send you a cheque if you give me your address and i will put in an extra 5 pounds to take extra care in wrapping it up. 

You will need lots of bubble wrap and two boxes that are much bigger than the sign its self. 

I would go as follows.

1, Wrap pediment in bubblewrap. 
2, place a piece of thin wood over the glass.
3. Wrap with more bubble wrap and put in box 1
4, Pack box 1 with paper.
5. Place box 1 in box 2 and pack with paper
6. Mummify box 2 with parcel tape
7. Do not mark down with true value and do not mark fragile

Please make sure that the item is far from touching the box as couriers can be pretty rough

www.transglobal.org.uk is the best way of sending parcel.

Sorry to be a pain, but I really don't want to lose a 100 years of history

Best wishes

Al.