*Mackem is capitalised as it's a proper noun.
It's quite clear the sign should say 'MACKEMS ON TOUR' as 'MACKEM IS ON TOUR' is just silly. I suppose looking at your fans attempts at bed sheets in the past I shouldn't be surprised.
I'll let your puerile comment on schoolchildren go.
I was giving an interpretation of the possible correct use of the apostrophe, not commenting on the validity of the statement.
And yes, my comment was puerile and borderline offensive but was added to highlight the foolishness of stereotyping the many due to the actions of the few which you once again do with your bedsheets remark (Ironic considering the subject of the discussion).
I come in peace, anyway If we're looking to critique each other based on the spelling and grammar of those for whom household linens are a canvas then I think we shall all lose.