Greytown's Cobblestones Museum and Tauherenikau's Tin Hut restaurant say consent was given to them in the past.
The council's planning and environment group manager Murray Buchanan said the council and the businesses are now searching their records.
He said if there was a consent, it could be 20 or 30 years old.
"To find it could be quite difficult."
Mr Buchanan said the District Plan allows for temporary signage to advertise an event, such as a race meeting at Tauherenikau, 28 days prior.
"The race course is quite happy with that."
With other remaining signage, Mr Buchanan said they will be doing a drive-around soon to establish what is left.
"The council has made these rules for a reason," said Mr Buchanan. "If you are trying to be a tourist area, it's retaining that character that attracts the tourists."
He had been anticipating a fight with two businesses, who were refusing, but their signs came down a week ago.
"We had been hoping to get compliance by co-operation."
A company who persisted with a definite non-complying sign would start receiving infringement notices of $300, issued daily.
"And we have the option of prosecuting, which opens up the option for maximum fines.
"In the next day or two, we will be doing a scout around, see what's still up."
