Yes, I mean the other smiley faces (☺☻), the heart symbol (♥), and many others (♪☼♂...) !
These are known as Alt-code characters, and they've been around for a very long time.
Although we now have Unicode that allow for thousands of different characters and symbols, for a long time computers could only represent 255 different characters. Besides the regular symbols, letters, numbers, and punctuation marks, a few of them represented codes that had no visual meaning, like "end-of-line", "carriage-return", and the like...
But, even though they had no visual representation didn't stop engineers from placing some nice visuals on it. :)
So... how can you type these weird and secret strange characters? It's quite easy...
You just need to press and hold the ALT key while you type its "alt-code" number in the numeric keypad.
Just try it: place your cursor in a text input area and press and hold the ALT key, and press the "1" key in the numeric keypad (make sure you have "num lock" on, so you can type numbers instead of using it as cursor keypad.)
ALT + 1 gives you: ☺
ALT + 2 gives you: ☻
ALT + 3 gives you: ♥
and so on...
Here's a table of most useful secret alt-code chars available:
From the code 32 (space character) up to code 127 you get the regular numbers, letters, punctuation marks and symbols. From 128 to 255, you get some few extra characters, like accented characters used in other languages (like: áêü) and some more symbols (µ¼Σ√...)
A few other useful symbols (you do need to type the leading zero in the alt-code):
Hope you find it useful! :)
P.S. If you're looking for other symbols like Apple's logo, be sure to check the Emoji and Glyphs page.