I had to say shirt because there isnt a Middlesbrough flag. Ok lets say for 111 years the Transporter bridge as it actually appears and looks in the flesh was on all Boro shirts over that period. As far as im aware its always been painted light blue and its appearance as never changed. Its Teessides bridge, Middlesbrough's bridge and a symbol of those who worked their guts out in the steel works. Its makes us proud, thats why its still standing. What else can we point as a symbol over such a prolonged period?
Lets paint it pink , totally change its design and shape, so it looks nothing like it is and stick it back on a Boro shirt. Or what about the Eston Hills . Infant Hercules and all that ! Lets say an image of those in black had been on Boro shirts for 134 years but then it was replaced with a pink Silhouette of Mount Kilimanjaro.
Doesnt matter though does it , its only symbolism and means nothing.