I'd like to put up a small ad that -- while for a third-party commercial venture -- is relevant to my own blog. I write extensively on Mexican history and culture. As a result, I've been contracted by a small Mexican publishing house to write a few pamphlets on those subjects, the first coming out at end of September. This first pamphlet is a tie-in to a historical exhibit and is written more to create an interest in the historical figure than to make any money.
Frankly, I expect I earn more from my paypal donate button, but -- whine and threaten as I do -- those are "voluntary" contributions, and not really a commercial ad.
Any problems with this, or do I need official blessings from the Pope of WordPress?