You can set up a Custom Rule for Events that looks for any Citation of several conditions. Such as Events that have certain Sources… or number of sources… or quality of Citation.
Normally, filters are used to limit which records are displayed in a view or are exported/printed. But you can also use the Add/Remove Tag addon Tool to add a Tag to the records. And you can use the Edit → Organize Tags to set a contrasting color and priority for tagged records.
And if you’re up for trying some bleeding edge addons, the CardView experimental addon has views with more visual indicators for secondary objects attached to People
