How to emphasize is sort of part and parcel to the message, which naturally has a certain font rendered to express the message.

Usually, and again, depending on the typeface, the bold member of the family is way too heavy, and usually ugly.

It's hard to make a general suggestion here, because I don't think there's a universal "Good Taste" rule to be applied here, because sign-making usually has a different set of aesthetics and a different target audience, then, say, a book or magazine article.

Is a swash considered the same, or close to an underline? I think a good swash, such as Letterhead Fonts offers with LHF Pilsner, is a good way to emphasize something on a cereal box or a poster.

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I think typography, as with any art, depends a lot on composition. You can force a word to have more significance by use of size, color, font, position, and so on.

-g-