I am curious as to what the passport entry stamp for the Bailiwick of Guernsey and Bailiwick of Jersey look like. I would assume that I would receive a stamp if I enter from France since I am leaving Schengen and entering CTA. I've tried searching but surprisingly can't find anything.
Below is the entry stamp of Alderney (Bailiwick of Guernsey) - a UK stamp but with crowns rather than stars to designate officer ranks.
Passports of EU/EFTA states are not stamped, nor are passports accompanied by an Article 10/20 card. However, the officer had no problem giving me the stamp (which is on a blank sheet).
You will not necessarily receive a stamp. I have travelled from Schengen to CTA (both UK and Ireland, and also from the UK on to Isle of Man, Jersey and Guernsey) multiple times and have never received a stamp.
It may depend on your citizenship.
I think you can ask on arrival if they can stamp your passport. I heard from some travellers that they like to collect the stamps and usually are able to get their passports stamped on request.
I just found a better answer to your question:
In addition, Guernsey, Jersey and the Isle of Man apply UK entry regulations and issue UK entry stamps in passports. Consequently, the UK is henceforth taken to include these territories.
So, the stamps would presumably look like UK stamps, with text referring to the respective location.
An Example can be seen below in the answer of Crazydre - it shows that the stars in normal UK stamps are replaced by crowns.
As MJeffryes mentions in a comment above:
This Home Office document mentions the stamps, but the photos have been redacted.