Technically, no. First because not all jars "ping". Second because sometimes jars will ping and then release and then ping again. Third because some will ping and then let go several hours or days later. So the "ping" sound is not the true test of a seal.

The NCHFP instructions for testing a seal:

Testing jar seals

After cooling jars for 12 to 24 hours, remove the screw bands and test seals with one of the following options:

Option 1. Press the middle of the lid with a finger or thumb. If the lid springs up when you release your finger, the lid is unsealed.

Option 2. Tap the lid with the bottom of a teaspoon. If it makes a dull sound, the lid is not sealed. If food is in contact with the underside of the lid, it will also cause a dull sound. If the jar is sealed correctly, it will make a ringing, high-pitched sound.

Option 3. Hold the jar at eye level and look across the lid. The lid should be concave (curved down slightly in the center). If center of the lid is either flat or bulging, it
may not be sealed.

It is also recommended that you test seals by carefully lifting the jar with your fingertips by the lid. Do it over the sink or a bowl in case the seal is poor.

The problem with jars that have tipped is that some of the food gets under the lid, between the lid and the jar rim, leading to weak seals prone to separation.

When in doubt, refrigerate.

Dave

Conversely a lid may "ping" and there's a good seal, but that doesn't mean the product itself is safe to shelve as it may have been improperly processed.

Since we're talking jam here, assuming it's a high-acid fruit and full sugar (i.e. "regular" jam) you can go ahead and leave it out and see what happens. There's no food risk and refrigeration at this point isn't necessary. You might just get lucky despite the jar's tipping, but if the seal holds and it is shelved, I'd move it to the front and mark it so it is consumed first. A seal like that is likely a bit weaker.

Carol

It was a full-sugar raspberry vanilla jam, so it's great to know that I'm ok to leave it out and check the seal tomorrow as planned. A big thank you to both of you - you're always so helpful!