While colleges have the budget to have a professional graphics department oversee the licensed used of their mascot to ensure it's consistency and integrity, high schools do not, and typically rely on generation after generation of student volunteer artists to create art for t-shirts, banners, the yearbook and other school projects. The problem is the lack of consistency. If you had 100 artists draw a panther, they'd all look completely different - each with their own style; and inconsistency is the single biggest factor in deteriorating a brand. The Pillsbury Doughboy doesn't look a lot different now than he did 50 years ago, and for good reason.
Picking your own format for your own special kind of card, the materials you are going to use and especially the message you are going to include is very important. Collect greetings and card stock materials and decide the layout and themes you want to use.
Yes, many think that branding is only important in fast food and retail operations, but it's extremely important to colleges that have to compete for student tuitions; and it's even gaining importance among high schools, and their surrounding communities, that are vying for prestige to boost neighborhood reputations/value. More successful high schools are now recruiting star athletes and students with high academic achievements, and the school's reputation can either help or hurt those efforts.