When the Allied officers rung the bell to go over the trenches, did they shoot the soldiers who disobeyed? I've always heard of Russians doing this, but I've never heard about any allied officers doing the same.
These answers I've given before should be pertinent; /u/elos_ and /u/NMW could probably also comment.
As to your question:
When the Allied officers rung the bell to go over the trenches
Whistles were typically used, but given how cliché they are, and the shift away from trenches by 1917, I can't imagine they were terribly common.
did they shoot the soldiers who disobeyed?
No; for one thing, even among soldiers that received the death sentence, I am aware of no soldiers, certainly in the Franco-British forces, that flat out refused to go over the top, with the exception of the French Army Mutinies in 1917, and that did not result in mass shootings. More so, in the British Army there was a complex legal process to go through, that was actually quite fair; only 10% of those given the death sentence (346 out of 3080) actually were executed.
There were a good number of summary executions in the Italian army, particularly during the Battle of Caporetto and other exceptional circumstances. Other measures included shelling or machine-gunning troops that surrendered, which godfather of fascism Gabriele d'Annunzio bragged about post-war.
Sources:
Mark Thompson's The White War: Life and Death on the Italian Front 1915-1919
John Schindler's Isonzo: The Forgotten Sacrifice of the Great War
As an aside, Russia was Allied.