Fundraisers at Stella Maris in Ramsey are requesting the return of a flag and banner.
The thieves stole the Manx flag and a donated Yamaha banner possibly along with other items from the site last night (Thursday).
Organising marshals say around 100 people are at the big grandstands at Stella Maris and they would like the items back.
They say there's been a great spirit as they raise money for the Greyhound League Isle of Man and the thoughtless action marred what was an otherwise enjoyable day.
'Possibly the most prolific drug dealer the island has seen' sentenced
Ramsey MHK resigns from departmental posts
Analysis: Could the next Budget leave you with more take-home pay?
Jail for mother who violently shook her infant son
Friday sailings in doubt