[UPDATE: The Apple Store is back up with a new version of Aperture but no new MacBooks. Apple’s press release introducing Aperture 3, the latest version of its high end photo editing and management software, crossed the wires at 8:30 a.m. ET. ]

The yellow “We’ll be back soon” sign — the universal signal of an impending product release — appeared Tuesday morning on Apple’s (AAPL) online stores around the world.

Speculation, echoed in a thousand tweets, centered on the MacBook Pro, which is overdue for an upgrade. According to MacRumors’ Buyers Guide, the product hasn’t been refreshed for 246 days. (On average it’s been getting an upgrade every 200 days.)

On Monday, Silicon Alley Insider passed along a report in a French blog that Apple was set to announce new MacBook Pros on Tuesday to coincide with opening day of Macworld Expo 2010 in San Francisco.

For more than a decade Apple was the centerpiece of the annual trade show, kicking off the expo with a Steve Jobs keynote and dominating the floor with a huge display of products. In late 2008 the company announced that Macworld 2009 would be its last.

See also:

• Five things to watch for at Macworld
• Behind Steve Jobs’ Macworld exit
• Why investors are better off without Macworld

[Follow Philip Elmer-DeWitt on Twitter @philiped]