We make liberal use of emoticon statuses in Slack: the 'away' icon (red circle with a line) is extremely visual and obvious for us to know which staff are out, sick, busy.. It's become like closed doors for us over time as we all agree to respect it.

It probably helps we are over several timezones and each work irregular hours according to what's happening (kids pick up, teaching, sports..): we can't count on who is there at any time and consequently run the business asynchronously except for pre-planned meetings.