Events with active* event signups show a flag icon in their title bar. While you can scan events in any calendar view and look for the flag icon, Table view is particularly good for quickly finding events with signups.
You can toggle calendars, adjust the date range, and use filters to show only relevant events, then quickly scan the Title column to see which events show the Signups flag icon.
Tip: Make the Signup column visible to see the number of signups for each event.
*Active signups means that the signups are still open; the flag icon will not show once the deadline has passed or the maximum number of signups is reached.