There are many online clipart services that provide excellent clipart for rubber stamping; the best images are from services that are subscription based that charge a yearly or per image fee. If this does not suit and you really want to save money you should find out which service your rubber stamp manufacturer belongs to, it costs nothing to search through the clipart service that he belongs to as he will be the person downloading the images. This bit of lateral thinking and finding the right manufacturer will save you lots of money because you will never have to pay for the clipart. Clipart.com is one of the best services that some manufacturers subscribe to; I estimate that over 3 million images at Clipart.com are suitable for stamp production and they are fine with manufacturers using the images for rubber stamps.
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.
Do make sure your cartoon advertising character is executed in a variety of poses so you can use him in a wide array of applications.