For the first time in 30 years I read the season ticket T&Cs recently. They say "Save for Away Fans, any attempt by a Named Ticket Member or Guest to gain access to the Stadium wearing or carrying apparel that demonstrates support for any football team other than the Club may result in admission being refused or that Named Ticket Member or Guest being ejected from the Stadium and in such circumstances no refund or alternative seat will be offered." So maybe you're right about your Scotland shirt. Likewise my son's Ireland shirt with "Coleman" on the back. I suspect enforcement will be selective though...