After upgrade from Linux Mint 19.0 "Sarah" to Linux Mint 19.1 "Tessa" the Dropbox icon no longer shows on the Cinnamon desktop panel . To fix this problem I carried out the following steps.
1) Stop all Dropbox elements running
$ sudo killall dropbox
$ ps -ef | grep dropbox
dobriain 9487 1785 0 10:20 pts/2 00:00:00 grep --color=auto dropbox
Dropbox is no longer running.
2) Start using the dbus-launch
This will launch a session bus instance, set the appropriate environment variables so dropbox can find the bus, and then execute dropbox with the start argument.
$ dbus-launch dropbox start &
[1] 9741
$ ps -ef | grep dropbox
dobriain 9642 1 93 10:24 ? 00:00:49 /home/dobriain/.dropbox-dist/dropbox-lnx.x86_64-63.4.107/dropbox
dobriain 9767 1785 0 10:25 pts/2 00:00:00 grep --color=auto dropbox
3) Disable Dropbox startup preference
Click on the dropbox icon that appeared on the desktop panel. Select "Preferences ..." and under "System" uncheck the box "Start Dropbox on system startup".
4) Create system startup for Dropbox
Now run the following command to create a Linux Mint autostart.
$ cat <<EOM >> ~/.config/autostart/dropbox_launch.desktop
[Desktop Entry]
Type=Application
Exec=/usr/bin/dbus-launch dropbox start
X-GNOME-Autostart-enabled=true
NoDisplay=false
Hidden=false
Name[en_GB]="Dropbox launch"
Comment[en_GB]="Launcher for Dropbox"
X-GNOME-Autostart-Delay=0
EOM
This creates a file in your home autostart directory and after reboot Dropbox will start automatically.
Happy days!!