At the very least, require that the front have an indication as to where the "information" is, which would be somewhere that can be read even if the paper has a band or tape holding it shut, or is in a plastic bag (some places do sell newspapers in plastic bags). The info would be about the slant, but also about what entity or entities either own it, or are the "primary supporters" (in the case of any theoretically "non-profit" paper, this would be even more important. But it would also let you know what companies or parties are paying the bulk of the revenue, so that the buyer can be informed).

Is it true that there's one newspaper in the UK that lets you know what party is in power just by looking at the title? (Next to the title is a picture of a warrior, if the Conservatives are in power, he's holding a sword and shield, if Labor is in power, he's chained up. Methinks said paper is either pro-Conservative, or anti-Labor)