Most client has a special command /me which will be replaced to message sender's nickname in the chat transcript and such message is displayed in special color (pink in Spark). Spark is not replacing /me command in toast popups. So, currently it is displayed like "username says: /me going to bed". I have filed this as a bug some time ago. Though now i feel this could be more as a trivial improvement, if needed at all. Because popup already shows who has said the message. Also one can see that someone has used /me command, without even looking in the chat window.
I wait for suggestions on this. Maybe this could be closed without any changes. Of course such message could be shown in popup like "username is going to bed" and maybe in pink color. Would be nice, but maybe not worth coding