The winter transfer window wasn’t a good one for Celtic and it was always the case that fans of the club would make their feelings clear at matches. A failure to maximise the club’s resource advantage over other teams in the Scottish Premiership has again frustrated many, especially when there are glaring weaknesses in Brendan Rodgers’ squad. The manager himself has spoken about his belief that the club can be braver in the transfer market, as he seeks quality additions to his squad. On Saturday, at Pittodrie, some Celtic fans unveiled a banner which stated “Celtic Board – On Your Heads Be it”…