The cartoon depicts Atticus as a boy rather than a man, barefoot and in short pants (back then, *only* boys wore shorts). It also pokes fun at his diligence to his studies rather than paying attention to pretty girls around him. The message is that he is not "one of us." He is far too absorbed in things no one else cares about.
Here is the text of that passage. Scout is the speaker.
We were surprised one morning to see a cartoon in the Montgomery Advisor above the caption, "Maycomb's Finch." It showed Atticus barefooted and in short pants, chained to a desk: he was diligently writing on a slate while some frivolous-looking girls yelled "Yoo-hoo!" at him.
Political cartoons such as the one about Atticus in the Montgomery Advertiser are perfect examples of satire. Satire uses humor or wit to expose, denounce, or show the irony of a situation. One interpretation of the cartoon is that Atticus is a diligent schoolboy; but another might be an allusion to slavery. The irony would be that as Atticus prepares to defend a black man, he's working like a slave to do it. Yes, schoolboys at that time wore short pants, but the cartoon also shows Atticus without shoes. The absence of shoes, plus short pants and the chain can suggest to the mind an image of slavery. The part with "frivolous-looking girls" yelling "Yoo-hoo!" certainly does suggest that Atticus is missing out on life (116).
Jem's interpretation is the best, though, when he says the following:
"That's a compliment. . . He spends his time doin' things that wouldn't get done if nobody did 'em" (116).
Atticus is fortunate to have such good kids who stand by him no matter what. This is definitely a difficult time for Atticus, but if anyone can handle it, he can.
This cartoon appears in the paper of the state capital, Montgomery, when Atticus is away for two weeks dealing with matters of 'emergency legislature'. It is the time of the Depression and there are mounting social and economic problems that Atticus has to help the state legislature deal with. Scout observes that 'these events were remote from the world of Jem and me.'
Atticus, then, has important work to do outside of his native town of Maycomb, although it is rather a different kind of work from the more dramatic events associated with Tom Robinson's trial. This is what the political cartoon is all about. It shows Atticus 'chained to a desk' and 'diligently writing', which illustrates how dedicated he is to his work, even if it may be 'dry' (to quote Jem) and boring: dealing with taxes, and so on.
The cartoon shows that Atticus is committed to even the dullest parts of his job, and that he is not distracted by more 'frivolous' pursuits (he pays no attention to the girls calling him). The cartoon also depicts him in a rather ridiculous light by presenting him 'barefooted' and 'in short pants' as though he were a boy. It seems to be playing on the image of the serious studious schoolboy who refuses to take part in the more lighthearted, fun-loving activities of his peers.