Signpost Corner, Road curve on Snaefell Mountain Course, Isle of Man

Signpost Corner is a road curve at the intersection of A18 Snaefell Mountain Road and A39 Hillberry Road in Onchan parish. The junction features directional signposts that mark where these two routes meet on the mountain roadway.

The site developed as part of racing operations in the mid-20th century and was adapted to meet the needs of organized events. Road modifications came in 1953, when the section was widened and reshaped to improve conditions for the motorsport activity.

The name comes from the signal station that relayed race progress by telephone to the scoreboards on Glencrutchery Road. George MacDonald Fraser, author of the Flashman books, titled his 2002 memoir of Hollywood scriptwriting "The Light's On at Signpost" after the site. Nearby Bedstead Corner is named for old bedsteads once used to patch a farm wall.

Signpost Corner sits at the A18/B11 Avondale Road junction, where riders approach from Cronk-ny-Mona over a blind crest about 200 metres before the bend. The corner is a 105° right-hander with a descent that makes it easy to enter too fast; riders who run wide can use Avondale Road as an escape route, so no spectators are allowed there. The junction was altered and drainage and road surface improved in winter 2010.

The signal station was first set up at Governor's Bridge and only moved to Signpost Corner as race speeds rose; it has since been shifted further back to Cronk-ny-Mona. The junction itself was added to the TT course in 1920, when the route was extended to its present length.