Identags are for TCA members. Part of being a member of TCA is agreeing to accurately represent train items you are selling, and to document alterations (repaint, aftermarket parts etc.) by affixing a TCA Identag to the item. Unless you are a member, then I guess there's no "need" to document your items as being altered. To many tinplate collectors, having original, un-altered trains is important and the hunt for those trains is part of the enjoyment of the hobby, and buying trains from a TCA member should give a level of confidence that the items being purchased are accurately represented. To me, as primarily a tinplate collector/operator who prefers originals (as opposed to reproductions/restorations), that is one of the main benefits of TCA membership, which is why I buy prewar trains only from TCA members. Sure, there's always a chance that a TCA member would choose not to follow this rule, but at least you have a shot at accurate representation.