The phrase "assign letters" is correct and usable in written English.
You can use it when referring to the act of designating specific letters to represent something, such as in coding, grading, or labeling.
Example: "In this exercise, you will need to assign letters to each category based on their importance."
Alternatives: "designate letters" or "allocate letters".
If you were to assign letters of the alphabet to combinations of digits, and were to do this for all human alphabets, syllabaries, and ideograms, then you could fit any written character in any language to a combination of digits in pi.
No, actually the biggest worry I have about Mr. M is that he seems to have multiple personalities -- personalities that he likes to assign letters of the alphabet to.
Health inspectors assign letter grades of A, B or C to a restaurant, which can be found along with violations at New York City's government Web site.
Efforts to establish accountability, like performance bonuses for principals and teachers, sophisticated student data systems and report cards that assign letter grades for schools, have been a cornerstone of the Bloomberg administration's efforts to overhaul the school system.
The Obama administration proposed on Monday two alternatives to the window stickers in new vehicles, including one that would assign letter grades for fuel economy and greenhouse gas emissions.
They assign letter grades indicating the relative risk, from super-safe triple-A bonds to moderately risky triple-Bs to the most risky single-C bonds.
Going back to June 30 , 1998 we assign letter grades to a fund's performance in up markets (a C or better is needed) and down markets (a B or better qualifies).
Grading systems can assign letter grades and/or numeric points.
He assigned letters to these lines, by which some are still known, such as the D-lines of sodium, the G-band, and the K-lines of ionized calcium.
In this system, antigens were eventually assigned letters and numbers (e.g., HLA-B51 or, shortened, B51).
His catalogue assigned letters from the Greek alphabet to groups of stars belonging to the same visual magnitude class in each constellation, beginning with alpha for a star in the brightest class.
