There's a "pending save" countdown (in blue) after you make changes that tells you when your vote(s) will be saved. When it says "selections saved" (in black), it's saved. On desktop this is located next to "Your ballot" but on mobile it's higher up, underneath "N candidates" (and disappears after about 10 seconds).
You can refresh the page, and if your choices are still where you left them, you're good to go. (Otherwise, try again.) This is a little faster than waiting for the badge, and also works after you get the badge if you want to change your rankings.
This is, admittedly, a workaround. Many people find the current indication unclear and want it to be changed. See the Meta SE feature request Introduce a clear visual indicator that confirms that one's vote counts in the election.