Edinburgh Waverley was among 11 key stations on the Scotland to London line where rallies were held to encourage passengers to back calls for the route to remain in the public sector.
The UK Government intends to hand the East Coast franchise to a private bidder by February 2015.
FirstGroup has been shortlisted, as has a bid from Eurostar and French firm Keolis, and another from Virgin and Stagecoach. But more than 60 MPs from the Labour, Liberal Democrat, Green and SNP parties have signed an early-day motion calling on the Government to keep the line public.
Yesterday's protest, which was also held at stations including King's Cross, Peterborough, Doncaster, Durham and Newcastle, was timed to coincide with the start of the LibDem spring conference in York.
The East Coast Main Line has been in public ownership since 2009 after two previous private train operators were forced to bail out of the franchise for financial reasons.
In October, figures showed the East Coast Main Line paid £208m in premium and dividend payments to the Treasury in 2012/13.
Figures from the Office of Rail Regulation show the route received the lowest public subsidy of any rail operator by some margin. Last year Virgin Trains, which operates the West Coast Main Line, received seven times as much in taxpayer subsidy.
Critics claim the East Coast Main Line has one of the poorest punctuality records.