A handwritten note suggesting a "possible explosion during the Woodward Avenue Dream Cruise" was found Tuesday at the DTE Energy substation building on Brown Road, the Detroit News reported.
The newspaper said police suspect the note was a hoax, but the threat is a concern because the Dream Cruise -- set for this Saturday -- annually attracts about 1 million spectators and thousands more leading up to the event.
"This is a serious matter and pulls resources away from legitimate police runs," Birmingham Police Commander Steve Schettenhelm said. "We want to find the person responsible."
Schettenhelm said the note has been turned over to the Oakland County (Mich.) Sheriff's Office.