I always announce my presence via a /e or other actions if I am spying on someone.
It only seems polite to let others know. After all, they may not want that kind of interaction. This does mean that players can, and sometimes will, metagame and tactfully not mention things they otherwise would when I'm around.
But I perhaps naively feel that if a player is the type to metagame, perhaps I've chosen the wrong person to spy on and it's not right to mistrust people as a starting point.
It only seems polite to let others know. After all, they may not want that kind of interaction. This does mean that players can, and sometimes will, metagame and tactfully not mention things they otherwise would when I'm around.
But I perhaps naively feel that if a player is the type to metagame, perhaps I've chosen the wrong person to spy on and it's not right to mistrust people as a starting point.