[vfulco]

Go to some social/private/kids event at school for half a day and dress up in a suit. Wear it back to the office. Perceptive people/managers will start to worry. Works every time.

[chatmasta]

Isn't this answering the opposite question of what the OP asked? He does not want his managers to know he's pursuing another job.

Then again, maybe Poe's law applies.

[fiftyacorn]

also keep leaving your desk when your mobile rings, and look furtive when taking the call