Wow! A few blacks with Barbour signs? That's real evidence Barbour massively improved among blacks. Former congressman (and Clinton Cabinet member) Mike Espy, a black Democrat, endorsed Barbour and called him his "homeboy." Barbour worked hard for a higher share of the black vote, featuring an African-American doctor in one ad praising tort reform; he also bragged about the federal funds he directed toward black families displaced by Katrina.
So it's not too unlikely that Barbour significantly increased his support among blacks.