Question: I'm looking for a word to refer to the visual appearance of a word only. I'll use an example to help explain what I mean:

"bow" can refer to the action of bowing to someone, or to a bow that I add when wrapping a gift. "bow" and "bow" are homographs because they are spelled the same way, though they have different meanings and pronunciations, and we consider them two different words.

Then, define a "qword" as an ordered set of letters (and diacritical marks) combined according to the conventions of English. 

"bow" and "bow" are two different words, but the same qword, since they are both "b", "o", and "w" combined in the same way and in the same order. 

And "résumé" and "resume" are different qwords since they appear differently in written English, though people often write "resume" when they mean "résumé", and we have no trouble understanding what they mean.

Is there an existing English noun that means the same thing as "qword"? If there is none, a compound word or phrase would also be fine.

Answer: 
*bow* is a "string", to start with. 

We are looking at "meaningful strings" in the context of the English language. 

A "meaningful string" *can* have more than one meaning. 

To be precise we could say a "meaningful character string".
Homograph is what you want:

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> What are homonyms, homophones, and homographs?
>  Homonym can be troublesome because it may refer to three distinct classes of words. Homonyms may be words with identical pronunciations but different spellings and meanings, such as to, too, and two. Or they may be words with both identical pronunciations and identical spellings but different meanings, such as quail (the bird) and quail (to cringe). Finally, they may be words that are spelled alike but are different in pronunciation and meaning, such as the bow of a ship and bow that shoots arrows. The first and second types are sometimes called homophones, and the second and third types are sometimes called homographs--which makes naming the second type a bit confusing. Some language scholars prefer to limit homonym to the third type.
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<https://www.merriam-webster.com/dictionary/homograph>

From MW