Hi Phil,
We used to do quite a lot of these but stopped using composite for individual letters as it de-laminates.
Any locator will do, but make sure you use an adhesive that will grip the Dibond and the locator – 3M or Eurobond will have a product.
There is a grey double sided 3M Tape that will do this (can’t remember the code though- Jeaton’s Preston).
Bighead locators are the best failsafe – especially for larger letters
http://www.hall-fast.com/bighead-bondin … aded-studs
But my advise for a long term sign is to stick to unlaminated materials!
Gil