Set up a timer to check when user chat input is activated client side, when it is trigger a server event that would trigger an event on all other client's to show the icon. The hardest thing i see is showing the icon, but it still possible, you have to check if player is on screen, then get world from screen position and attach an icon to it. Just try to start getting the chat input atm, then go to syncing it and do the icon last. If you start it yourself and post the code you get im sure a lot of people, me too will be helping with it and show the right direction. Functions are documented on the MTA wiki. It's just the fact that you need the code, others are not obliged to go and write it.