plainbibliographystyle), or in the order of first citation (LaTeX's
alphabibliographystyle) or (Briggs et al., 1989), for the paper
Preston Briggs, Keith D. Cooper, Ken Kennedy, and Linda Torczon. Coloring heuristics for register allocation. In SIGPLAN '89 Conference on Programming Language Design and Implementation, pages 275--284, 1989.
When a backward computation algorithm constructs the entire dynamic dependence graph prior to slicing (e.g., Algorithm III in ), as our prior experience in  shows, for [...](wrong) in spite of using numeric labels, and I have also seen correct citations used with name-based labels. The sentence above should be something like:
When a backward computation algorithm constructs the entire dynamic dependence graph prior to slicing (e.g., Algorithm III of Agarwal and Horgan [AH90]), as our prior experience shows [ZGZ04], for [...]or something like
When a backward computation algorithm constructs the entire dynamic dependence graph prior to slicing (e.g., Algorithm III of Agarwal and Horgan (1990)), as our prior experience shows (Zhang et al., 2004), for [...]So, to get people to use the correct writing style, numeric labels are insufficient. We have to teach writing style to them.
But even if the claimed connection between label style and writing style existed, the readability advantages of name-based labels would trump such a minor writing style issue.
Also, authors may work around the unreadability of numeric labels,
resulting in much more space consumption than a label style like
alpha style. E.g., instead of
We compared a conventional colouring register allocator [BCKT89] to [...]an author might write:
We compared the conventional colouring register allocator of Briggs et al.  to [...]
I have ignored such a requirement a few times until now, and I have not received any comment from reviewers or publishers about that.
If you are preparing a paper for ACM proceedings, don't use the official sig_alternate.cls etc. style (which is broken in many ways in addition to not allowing the BibTeX alpha style); if you want you paper to look in the ACM style (except for citation labels), use Mike Sperber's sigplan-proc.cls style.
If you organize an ACM event, note that ACM actually does not require you to use their style (although that's not clear at first); at least that's what I found out pretty late in the IVME '03 game. Similar things probably apply to other publishers.