w10 + w11 displays the green [H] tray icon only for a short time in the tray.
To make it permanent visible:
¹click the tray menu ▲
²dragNdrop the Icon back to the tray
Windows 7 + XP
To change icon settings: show hide via .reg file
ALL Click on the arrow in the notification area on the taskbar, and click on "Customize"
Underneath the box with all icons there is a checkbox
Only the H icon: Click/tap on the Behaviors drop down arrow menu to the right of the icon select show icon and notification
TEXT + screenshots
http://www.sevenforums.com/tutorials/293-notification-area-icons-hide-show-system-icons-notifications.html