Tattoo should never be confused with tattoo. They are unrelated.
When a Dutch pub closes they toe (Dutch for shut) the tap (Dutch for tap). This is called the tap-toe or closing time.
In 1644 Colonel Hutchinson signed off some orders to the garrison of Nottingham. Order ten went thuslyly:
10. If any Taverne, Inne, or Alehouse soever shall sell any wine, ale, or beare (except upon an extraordinary occasion to one that is sick) after the houre of nyne of the clock at night, after the taptoo hath beaten, untill the Revelly hath beaten the next morninge, hee shall pay 1s., or suffer imprisonmt till hee pay the same; and hee who fetchets the drinke after the aforesaid houre shall pay 2s. 6d., or suffer imprisonmt till he pay the same [...] Whosoever shall give Information of any pson who shall comitt any of these offences, he shall have halfe the penalties sett upon them for his reward
Three things should be clear from this, dear reader: Colonel Hutchinson was a bad man, alcohol cures sickness, and the taptoo was now something that was beaten on a drum each evening calling the soldiers home from their taverns, whorehouses and book-groups.
From there, the army had only to alter the P to a T and extend and elaborate the evening drum-roll into the outer wildernesses of tedium, and you have the military tattoo.
Tattoo, on the other hand, comes from a Polynesian word tatu meaning to puncture or make marks on the skin.
This is a pity.
A military tattoo