Mathematicians' manual of style I know that there are many styles to write citations and footnotes and that they are all equally good (as long as the reference is complete), but I would like to know if mathematicians follow some particular guidelines. 
If so, can you add a link (or a reference) to a good handbook covering the details of "the mathematicians' manual of style"?
 A: This website, by Dr. Michael K. Kinyon (Wayback Machine),  has many resources which will answer your question; however, I no know of any MLA for math.
Math Write (Wayback Machine)  A huge collection of Books, Articles available for download or viewing, and Websites: about how to write mathematics.
Because this is not my own work, I suggest that if Dr. Kinyon is a user here, give him the bounty.
A: Many journals have a particular style for citations, but the style differs from one journal to another (or at least from one publisher to another).  When authors are left free to select their own styles, even more variation results.  
I've come to prefer a style in which (1) authors' names are given in full, including their first names if I can find them, (2) titles of articles or chapters are in roman type and enclosed in quotation marks, (3) titles of books and journals are in italics, (4) cities is which books are published are omitted.  I'm not sure I've ever met anyone who agrees with me on all of these. 
As for footnotes, most mathematics papers don't use them for pointers to the literature.  They're used mainly for tangential additions to the main text, and they are fairly rare (except for acknowledgements of grant support).  To refer to the literature, one would usually use a pointer in the main text; this can have many forms like [Blass and Sagan 1986] or [BS 1986] or [BlaSag 1986] or (my favorite) [3].
A: Halmos has a good guide to writing mathematics (Wayback Machine). Although it's old, it's still relevant. As far as citations go, though, it's usually up to the journal.
A: You can also read Terrence Tao's writing advices.
A: Another reference: Math into Type, published by the AMS.
A: One of Steven Krantz's many superb books is
A Primer of Mathematical Writing: Being a Disquisition on Having Your Ideas Recorded, Typeset, Published, Read and Appreciated
It is published by the AMS. Here is a brief excerpt to give an idea:

Here is the table of contents:

A: I've found Gillman's Writing Mathematics Well to be very useful.
A: 
Many of the answers provide good hints and valuable references. I'd like to point out to D. Knuth. We owe to him the

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*$\TeX$-Book
Besides many other treasures he gave us the language $\TeX$, the way of writing typographically beautiful and professional mathematical text. So, when talking about mathematical styles and conventions we should also mention the $\TeX$-Book. This is a great resource full of valuable information about how to write mathematical formulas and mathematical text in general. And - reading this book is pure fun!

Another interesting paper from D. Knuth is


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*Mathematical Writing.

This report is based upon a course named Mathematical Writing which he has given at Stanford University. This paper is full of highlights containing guest lectures from H. Wilf, Leslie Lamport ($\LaTeX$), Paul Halmos and others. It's as informative as funny to read how these great guys discuss stylistic issues.

Using a proper notation or following a specific writing convention may also be connected with semantic issues.


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*Bracket notation for the coefficient of operator
This a nice example of D. Knuth considering the pros and cons of a specific notation and which convention we might follow.


Additional hint: A nice overview containing some guidelines and good refs is Ten simple rules for mathematical writing
