Just wanted to clarify, do you mean things as false cannon? I ask because false guns were often pretty easy to spot when you were close to them, they seemed to be more designed to fool people at a distance. It seems that there wasn't a war in the age of black powder artillery that didn't feature the use of fake cannon (something like a log painted to look like a cannon and placed on a contraption resembling a gun carriage - and sometimes not even that). The name "quaker gun" is thrown around with these guns in American conflicts. That's the easiest answer that comes to mind (and probably the easiest to go find sources for right away). Here is a picture of a false gun from the confederate positions at Centerville, Virginia during the American Civil War.