The man was left with a black eye during the incident which happened in Park Road, St Annes.
The owner, who did not want to be named, had intervened after hearing a commotion outside the property.
He was then assaulted by the thugs with the four foot-long A-board.
The suspects, both believed to be in their mid 20s, escaped to a car shortly afterwards and drove off in the direction of Clifton Drive South.
The attack is the latest in a string of incidents of anti-social behaviour committed against traders in the town centre, according to St Annes Chamber of Trade co-ordinator, Arnold Sumner.
However, Mr Sumner has been quick to praise the response of the police following the assault.
He said: “The police have done a wonderful job and we’re hoping that they now have control of the situation.
“We are all too aware that we must address the issue of anti-social behaviour.
“The police are taking it very seriously and that situation has now got a lot better according to the other traders I’ve spoken to.”
According to figures released at a meeting of the St Annes Central Police and Community Together Team (PACT) last week, there had been 15 incidents of theft at properties in the town centre during the previous month, as well as nine assaults and eight cases of damage.
The police had also noted an increase in anti-social behaviour in the area.
A Lancashire Police spokesman confirmed the force was hunting for two suspects involved in the assault on the man.
He said: “We are appealing for information and anybody who can help us should contact us on 101.”
The next meeting of the St Annes Central PACT will take place at the YMCA, in St Albans Road, on Thursday September 6 at 7pm.