Ways of Indicating Sarcasm in Writing?

Almost all words can convey sarcasm, but the trick is in how you use them. Apart from italics and "quotes", a standard way of conveying sarcasm is the hyperbole, meaning that you very clearly overstate something - in case of sarcasm, to mean the opposite.

Be very aware that sarcasm is one of the most difficult emotions to convey in written (on-line) form - I see examples on a daily basis where sarcasm is not picked up by people on discussion forums and the like, which can lead to sometimes very annoying, weird or unpleasant situations. When in doubt, overdo it :

In this case, Layla accidentally made a mistake.
Yeah, that is a really smart thing to do, genius! Why didn't I think of that?

If you are writing to persuade, you can make a very clear sarcastic remark by arguing briefly for the extreme opposite. This will confuse the reader long enough for them to realize it's intended as sarcasm. For example, arguing against investment in a hypothetical country's infrastructure:

Many folks in this council are suggesting that we invest in our infrastructure but this will take away from our education budget.

Another reason we should not invest in better infrastructure is because our unemployment rate is the lowest in the world and we are in such a desperate need to provide jobs. We have too many teachers and not enough construction workers; teachers work best with class sizes of more than 200.