Check it out ... the singer, with the help of his sister, Aaliyah, draped the front yard of his L.A. pad in fake cobwebs Wednesday ... getting the abode ready for the slew of trick-or-treaters set to hit the streets Thursday evening.

As to why Shawn waited so late into October to decorate, it's safe to assume his tour -- which had him on the road for most of this month -- factored into his decorating plans.

The Canadian pop star surprised concertgoers at the Red Rocks Amphitheatre in Colorado this week when he opened up about his personal life mid-show ... sharing he was figuring out his sexuality, calling it "a beautifully complex thing."

While the remark took the internet by storm, Shawn is moving forward, choosing not to elaborate on the subject -- clearly focusing on Halloween, instead.

Shawn isn't the only celebrity getting into the Halloween spirit, either.

Several stars have already gotten into the spirit ... with Kylie Jenner dressing up as "Barbarella" and La La Anthony rocking a Lady Deadpool getup -- and drawing a ton of celebs to her Halloween shindig Wednesday night.