What’s more useless: this Fifth Avenue phone booth or the deer-crossing warning attached to it?

A head-scratching banner in the middle of the concrete jungle — Fifth Avenue and 15th Street — tells drivers to watch out for deer.

“I’m still on high alert to see my first deer in this city,” quipped Manhattanite Clare Tokheim, who saw the poster Tuesday and took a pic for social media.

“Watch out! Deer are more likely to cross the road at dawn and dusk,” says the sidewalk banner, which is facing south and not even visible to downtown-bound drivers.

The safety announcement directs New Yorkers to visit nyc.gov for more information “about living safely with deer.”

The site notes: “In New York City, white-tailed deer can currently be found in Pelham Bay and Van Cortlandt parks in The Bronx and throughout Staten Island green spaces,” none of which are anywhere near Union Square.

A spokesperson for the Parks Department said the agency places deer-crossing warnings outside the two boroughs — where deer actually live — when “capacity is reached.”

“Then some ads can end up placed in other boroughs,” spokesperson Meghan Lalor said.