In Windows 10 Insider Preview Build 15042 there was no watermark present on the Desktop. And there was no expiration date either.
Bad thing -it has again come back in Windows 10 Insider Preview Build 15048. And the expiration date for this preview build is 16th May,2017.
I am still trying to understand why did the watermark and expiration date vanish in earlier build and what made them reappear in Windows 10 Preview Build 15048.
I have no clues 😦