B. By urging fugitive slaves to avoid kidnapping and capture
Explanation:
If you look closely the poster is trying to warn fugitive slaves of the "kidnappers/slavecatchers". Therefore the other 3 don't make sense so the only logical answer would be B.
I think it is Lincoln because the term carpetbagger is a compliment and usually said to the Northerners who moved to the South after the Civil War took place.