Several photos from inside Miami's loanDepot Park showed the large signs being unfurled at the team's game against the Colorado Rockies.
One sign read "Trump Won - Take Back America" while another proclaimed "Proud Boys Did Nothing Wrong - Free All Political Prisoners 1/6/21" -- a reference to the date of the deadly riot at the US Capitol Building.
A spokesperson for the Marlins told WTVJ in Miami that at least five people were ejected from the ballpark because the signs violated their rules on banners, signs and messaging.
According to the team's website, signage or banners are not permitted to be larger than 3 feet by 5 feet. They also cannot contain any language that is political, the guidelines say.