Williams' wife, Amy, tweeted a picture of the black and white sign, which reads, "HAPPY BIRTHDAY DERON! from your Brooklyn family" and features the Nets' new logo.
The Nets are hoping to give Williams an even better present on July 1 when he becomes a free agent: a max contract extension.
Williams is expected to opt out of his contract and officially become an unrestricted free agent at midnight July 1.
Sources told ESPN.com's Marc Stein that Williams is only interested in re-signing with the Nets or playing for his hometown Dallas Mavericks.
The Nets are confident that they can keep Williams despite the uncertainty surrounding their roster.
But they are expected to be very active in the offseason in trying to put the right pieces around Williams, assuming they can retain him.
Mike Mazzeo is a regular contributor for ESPNNewYork.com.