The thief is being described as being black male, with short hair and wearing sunglasses with a black denim jacket and dark jeans and was seen around Portman Road at around 6:30 pm on Monday night
Police are appealing for anybody who sees anything suspicious in the area to contact them on 01473 613500 or Crimestoppers on 0800 555 111.
A spokeswoman for Suffolk police said: "Clearly these items have been left in remembrance to Sir Bobby Robson and it is not in the spirit for anybody to be going and taking them away. People have put these down in remembrance and it is the same as taking something from a grave."
A club spokesman has said: "The club has been made aware that a small number of items have been taken from the public tribute to Sir Bobby Robson and we are, naturally, distressed and disappointed to hear of the theft.
"It is our further understanding that Suffolk Constabulary are investigating the matter and as always we will be assisting them in any way we can to help them find those responsible."