How to package desktop file with external icon

edit

My desktop file has a line

Icon=preferences-system-notifications

There is no separate icon for the application and I want to use the icon provided by system. Checking DNF, I can see that this icon is provided by various packages:

# dnf provides "*/preferences-system-notifications.svg"
elementary-icon-theme-4.3.1-2.fc27.noarch : Icons from the Elementary Project
Repo        : updates
Matched from:
Filename    : /usr/share/icons/elementary/categories/32/preferences-system-notifications.svg

pop-icon-theme-0.1.0-0.3.20180405gitb1b46e8.fc27.noarch : System76 Pop icon theme for Linux
Repo        : updates
Matched from:
Filename    : /usr/share/icons/Pop/16x16/apps/preferences-system-notifications.svg
[...]

elementary-icon-theme-4.3.0-1.fc27.noarch : Icons from the Elementary Project
Repo        : fedora
Matched from:
Filename    : /usr/share/icons/elementary/categories/32/preferences-system-notifications.svg

numix-icon-theme-circle-0.1.0-14.git5a11140.fc27.noarch : Numix Project circle icon theme
Repo        : fedora
Matched from:
Filename    : /usr/share/icons/Numix-Circle/48/apps/preferences-system-notifications.svg

pop-icon-theme-0.1.0-0.1.20170831git38ecdfe.fc27.noarch : System76 Pop icon theme for Linux
Repo        : fedora
Matched from:
Filename    : /usr/share/icons/Pop/16x16/apps/preferences-system-notifications.svg
[...]

xenlism-wildfire-0-0.3.20160511gitd3b9ad2.fc27.noarch : Minimalist theme for your desktop
Repo        : fedora
Matched from:
Filename    : /usr/share/icons/Xenlism-Wildfire/Apps/preferences-system-notifications.svg

What is the correct way to express the dependency on external icon in a spec file? The packaging guidelines were not helpful for me