No single area of the Internet remains free from being subject to the influence of pornography and filth. Even the sweet and innocent smiley, the humble yellow smiley face we know and love has 'grown up' and moved to the Red Light District. No longer a naive and innocent emoticon, this little smiley has learnt to display some naughty behaviour.
If you use Skype on a Mac I found these instructions don't know if they work and they are a couple of years old. However, some other posts I saw would seem to indicate that while you might get them to work on your machine, your contacts will have to add them as well. If this really works, you could use whatever. You can download individual emoticons, but you'll have to scroll thru screens of them to find the ones you want. Supposedly, adult ones are removed, but I've not found this to be the case.