The phrase "thanks for returning" is grammatically correct and can be used in written English.
It is typically used as a way to express gratitude for someone's act of returning something that was lost or borrowed. Example: "I just wanted to say thanks for returning my notebook. I thought I had lost it for good, but your honesty saved me from having to rewrite all my notes."
Not for George the usual thanks for the returning officer's efforts.
The royals and other VIPs marched off to a grand lunch in the Guildhall, and the lesser mortals scattered to the pubs, cafes and restaurants of Leicester, whose owners are also giving devout thanks for the return of a king.
Many went to church to give thanks for their safe return and remember fallen friends.
He went to Catholic shrines in Venezuela to give thanks for his apparent return to health after an initial round of cancer treatments last year.
Violetta wants to go to a church to give thanks for Alfredo's return, but she is too weak even to dress.
It was the day the Massachusetts governor back in 1637 proclaimed a day of giving thanks for the safe return of a band of heavily-armed hunters who had just massacred 700 Pequot Indians.
Squires again interrupted, asking "What day was it that the young woman was robbed?" The answer came back, from the court: "She says on the morning of the 2nd of January", and Squires replied "I return thanks for telling me, for I am as innocent as the child unborn".
We give thanks for Jason's safe return.
We originally had an appointment that day, Ash Wednesday, when I already had her annual cake to give in thanks for her help on tax returns, and then she was standing beside a casket, preparing to say farewell, the ashes mixed with snow and hundreds of shell casings in Angelus Oaks above us.
In the new campaign, she is the face of the question "Are you wise enough?" She and Mr. Walke speak of children from old cases, now grown, returning to express thanks — for separating them from a drug-addicted parent, perhaps.
