Similar to the Miles & More offer that we saw earlier this year, Sixt is offering members of airberlin’s topbonus program 1,000 free miles simply for registering on their site for a frequent renter offer from them.
The sign up form is in German but is pretty easy to translate
topbonus nummer=topbonus number,
Sixt Card Nummer=Sixt Card Number (I don’t have one and didn’t fill in this box and it still let me register)
Sind Sie Sixt Neukunde?=Are you new Sixt customer
Finally be sure to check off the last box as that appears to be the key to earning the 1,000 miles. The miles should be awarded in 6-8 weeks
Here is my confirmation page screenshot: