Many email programs have "Urgent" or "Low importance" flags that you can mark your message with before sending. But often what the reader *really* wants to know is whether it's good or bad news.
If a manager has 100 emails in his/her inbox, his/her primary concern might be "what problems are occurring
today"? For that, he can jump right away to the "Bad News" flagged e-mails (those depicted with a :( face next to the subject line). Then s/he might see:
:( System Job #161A - failed to run, please call me
:( Joe, I forgot my password, what is it again,
:( Sorry, I won't be able to make lunch next Tuesday, let's reschedule for next week
Etc. Then the manager can instantly identify the day's problems.
Often, just the combination of smiley plus subject line will make the email's contents obvious. This saves the manager's time opening & reading every email the instant s/he receives it. For example,
:) Reconciliation of assets to liabilities
you know the email will say that blah blah blah the employee checked the reports and they matched.
:) My exam
Now you know your friend passed his exam, instantly, before even opening the message. Conversely, :( my exam
you can prepare yourself for the worst before being hit with it.
Not every email needs a :) / :( flag; it's optional to use one. Just as the "urgent" flag is optional.