What's the @ mean before things?

I've seen the @ sign before a lot of different syntax. What does it mean?

I was reading up on some MySQL references and saw it here

SET @str = BINARY 'New York';

but I've seen it in many other places as well and was always curious.

Hmm, the example you posted appears to be MySQL, but for PHP usage it is used to suppress error reporting. For example, if your script tries to read a file and the file doesn't exist you wouldn't want to display some ugly PHP error. Instead you would attempt to read the file (suppressing the error if there is one), then display a friendly error to the user:

More info in the manual:

PHP: Error Control Operators:

http://php.net/manual/en/language.operators.errorcontrol.php

Some quick examples:

SET @city = (select city_name from cities_table where id = 12321); -- pretend 12321 is the row for "New York"
select @city;
-- Returns 1 row: 'New York';
-- We don't need to reset the variable
select * from my_table where city = @city;

Just be careful, it works differently based on where it appears in the statement.