Green’s Dictionary of Slang

lord mayor n.1

[on pattern of alderman n. (5); citizen n. (1); gentleman n.: smaller and larger versions of the tool]

a large crowbar.

[UK]D. Stewart Shadows of the Night in Illus. Police News 7 Dec. 12/4: ‘Wielding a fearful weapon (his safe-breaking implement called the “Lord Mayor”) which was fashioned of steel’.
[UK]R.T. Hopkins Banker Tells All 137: ‘Is there a lord mayor as well as an alderman?’ asked the learned counsel.

SE in slang uses

In compounds

lord mayor’s coal (n.)

a piece of slate.

[UK]R. Barham Ingoldsby Legends (1866) 282: Had the coal been a ‘Lord Mayor’s coal,’—viz.: a slate;—What a different tale had I had to relate!
lord mayor’s fool (n.) [pvb ‘like My Lord Mayor’s fool, full of business and nothing to do’]

‘a personage who likes everything that is good, and plenty of it’ (Hotten 1864).

[UK]H. Kingsley Recollections of G. Hamlyn (1891) 309: Burnside was in the habit of saying that he was like the Lord Mayor’s fool – fond of everything that was good.
[UK]Hotten Sl. Dict.