When hosting a meeting with people coming late or leaving early, it's annoying to her either the participant's name or the 'ding' sound. Here are two ways to disable them while in a Lync Meeting.
1. DTMF Control
If you are dialed into the conference via your PBX phone or mobile phone, and are a leader/organizer you can press *9 to disable this. There are number of in conference DTMF controls listed on your dialin page (https://dialin.concurrency.com
2. Lync Meeting Options
While in a Lync Meeting on your PC, you can click the three '...' in the lower right hand corner of your conference window. Then you select Lync Meeting Options. Then just uncheck the Announce when people enter or leave option. Make sure to click OK.