Maybe because these two racial groups have had low voter turnout in the past..
Hmmm, I guess that makes sense, although I'm not seeing a clear trend indicating that, unless I'm misinterpreting the data here...
http://www.census.gov/hhes/www/socdemo/voting/publications/p20/2008/tables.html
White non-hispanic
Reported Voted Did Not Vote
Number Percent Number Percent
100,042 66.1 51,279 33.9
8,414 49.4 8,602 50.6
30,201 62.1 18,432 37.9
39,946 71.2 16,123 28.8
11,706 74.7 3,967 25.3
9,776 70.2 4,155 29.8
Black
Reported Voted Did Not Vote
Number Percent Number Percent
16,133 64.7 8,797 35.3
2,161 55.4 1,736 44.6
6,149 64.0 3,462 36.0
5,721 68.7 2,609 31.3
1,291 70.9 528 29.1
812 63.8 461 36.2
Hispanic
Reported Voted Did Not Vote
Number Percent Number Percent
9,745 49.9 9,792 50.1
1,376 38.8 2,169 61.2
4,028 47.7 4,408 52.3
3,141 58.1 2,269 41.9
720 59.6 488 40.4
481 51.3 457 48.7
EDIT: Well, ok, latinos clearly vote a bit less, but blacks seem more or less on par.
Again, check the lower pic in the article.
I did but it's irrelevant to the point I'm making (although maybe it's not clear in my op). I know that racists and racially-minded people exist all over the place, but making up slogans and signs to be used for official campaigning purposes goes beyond.