Typical plural mistake - documented!
This is a typical mistake: using an apostrophe to create a plural form. Why do so many people do this? And it's a business--you'd think they'd proofread their sign before putting it up for all the world to see. And the team is called "Cubs", not "Cub". Bottom line: this is lame, especially because it's on a public sign on a major street in a major city.