A spyglass was a kind of telescope used by pirates and sailors alike to spot dry land or to see any trouble that might be brewing in the distance. Such a name, then, is entirely appropriate for Long John Silver's place of business, as he always wants to see what dangers might be lurking on the horizon.

The inn gets its name from a couple of two slit windows that allow Silver and the patrons of his tavern to spot any members of a press-gang that might be lurking in the vicinity. A press-gang was the name given to a group of sailors who'd prowl around the docks looking for potential crewmates for a forthcoming voyage.

These sailors would often approach drunks in taverns just like The Spyglass Inn and put a shilling into their hands. This would then mean that they'd accepted the king's shilling, as it was called, and had therefore agreed to serve aboard one of His Majesty's ships. Before they knew it, these poor wretches would find themselves on board a ship, nursing a blinding headache, and realizing to their horror that they were trapped. If they tried to escape, they would be hanged for desertion.

The last thing that Long John Silver or any of his patrons wants is to be pressed into service like this. Hence the importance of having discreet holes in the wall that allow people to see if any men from the press-gang are hanging around.