Issued in 1998 by Mongolia, the American rock band the Grateful Dead's dancing bear mascot was pictured participating in several sports, one of which was soccer. Although I don't know if any of the members of the Dead have an interest in soccer, they have supported the 1990 Lithuanian Olympic Basketball team, including their wearing tie-dyed jerseys.
Several members have also sang the national anthem at San Francisco Giants games..
Countries like Mongolia often issue stamps not for their postal validity, but to bring in revenue from collectors...