Any attempt to tag a runner should get a call, whether safe or out. If the fielder swipes at a runner and misses, and it is at all close, and there is not an immediate follow-up tag attempt, the covering umpire should signal safe. This only indicates that the specific tag attempt was unsuccessful, and the runner is still in play.
However, if there is an immediate follow-up tag attempt, the covering umpire should use “timing” and wait until all associated action is complete before making a visual ruling. As above, if the tag is missed, the signal is safe. If the tag is applied, again, use timing and make sure the fielder maintains his possession of the ball until the release of the ball is voluntary and intentional before making the visual out ruling.
The key is timing. Don’t be or get in a hurry. Let the play happen, see the whole play, and make one signal, and get ready for the next play, which may be another tag attempt.