To tip the lion; to squeeze the nose of the party tipped, flat to his face with the thumb. To shew the lions and tombs; to point out the particular curiosities of any place, to act the ciceroni: an allusion to Westminster Abbey, and the Tower, where the tombs and lions are shewn. A lion is also a name given by the gownsmen of Oxford to an inhabitant or visitor. It is a standing joke among the city wits to send boys and country folks, on the first of April, to the Tower-ditch, to see the lions washed.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Linen Armourers * LiquorNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes