You don't want to do that. If they require you to sign something in writing, that will be used as persuasive ammo on a petition or otherwise which will be handed to anti-gun legislators. Just don't do business with that animal shelter. While these places call themselves "not-for-profit" - they make money in fees and donations, and distribute this the people in charge in the form of salaries. Don't so business with anti-gun wack-jobs.