Last week we told you about how Marcus Books, the nation’s oldest black-owned bookstore, is taking on Amazon.com’s new price-checker app. Now, the indy bookstore’s supporters have launched an online tool that reminds prospective shoppers that it’s important to support local businesses in person this holiday season.

Jasmine Johnson, whose family has run San Francisco’s Marcus Books since 1960, started a Change.org petition last week to call out Amazon’s shadiness. The app in question allows customers with smartphones to walk into local bookstores and compare prices with the online retailer. It’s considered an especially low-blow by independent bookstores, many of whom are already struggling to keep their stores afloat.

"All around the country I see independent bookstores and other retailers fighting for survival in this tough economy," Johnson wrote in the petition. "Amazon’s Price Checker app goes beyond simple competition in a free marketplace. It represents an ugly race to the bottom that might provide short-term benefit for bargain hunters, but will lead to long-term pain for communities in the form of lost jobs and tax revenues."

Shoppers can use Google’s Chrome Web browser to help bring that message home. The program is called "Amazon, huh?" Here’s how it works: Customers can download the Chrome extension, and each time they log on to Amazon.com, the Marcus Books logo pops up on the far right side of the browser. Once users click on the logo, they get this helpful reminder:

The extension was created by Josh Begley, who’s studying interactive telecommunications at NYU. "It’s basically the same thing that Amazon did, but in reverse," Begley told Colorlines.com about the tool. "Amazon’s smartphone app was one of the first times they’d stepped into local bookstores, so this is a way for supporters of those bookstores to step into Amazon."

"There’s nothing like being in a bookstore," Begley continued. "So in addition to cracking on Amazon, [the tool] is a friendly reminder to shop at local businesses this holiday season — especially ones that have been around since 1960."