libindicator3-7 software package provides panel indicator applet - shared library, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install libindicator3-7
libindicator3-7 is installed in your system.
Make ensure the libindicator3-7 package were installed using the commands given below,
$ sudo dpkg-query -l | grep libindicator3-7 *
You will get with libindicator3-7 package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | Libraries |
| Package | libindicator3-7 |
| Version | 12.10.2+16.04.20151208-0ubuntu |
| Description | panel indicator applet - shared library |
| Sub Section | Libs |