Can I learn sigil sequences for teleportation circles before learning a spell that can use them?

Question

Suppose I plan to learn the teleportation circle spell, or another spell that can use teleportation circles, some time in the future, but I don't currently know any such spell (or have one in my spellbook, if I'm a wizard). Can I start collecting known sigil sequences now and then use them once I learn the spell, or is knowledge of the spell a prerequisite for comprehending the sigil sequences?

For a specific example, would the following sequence of events be possible?

1. Visit a town and learn the sigil sequence for a teleportation circle there.
2. Leave the town and go adventuring.
3. Learn the teleportation circle spell during the course of my adventure (having not previously known any teleportation spells)
4. Use the spell to return to the teleportation circle in the town whose sigil sequence I had previously learned?

Answer 1

It's up to your GM

The details of learning sigil sequences is entirely absent from the rules. Apparently this was intentional on the part of the developers so that a GM can limit access to teleportation circles in areas the GM does not which to be accessible at a given time. This is discussed by Jeremy Crawford on Dragon Talk on 7/23/18.

...well only if you know that sigil sequence and that's in the hands of the dungeon master whether whether [sic] the DM is ever going to allow that that [sic] very useful piece of information to fall into your hands

Answer 2

All indications suggest this can work. It can also be very dangerous.

If you know the sigil sequence at a permanent location, the spell description indicates you should be able to create the circle and transport to the permanent teleportation circle.

As you cast the spell, you draw a 10-foot-diameter circle on the ground inscribed with sigils that link your location to a permanent teleportation circle of your choice whose sigil sequence you know and that is on the same plane of existence as you.

Some important factors:

• What is the visibility of the sigil at its permanent location? It may be hidden, partially-hidden, invisible or difficult to discern by either/both magical and non-magical means. This could affect your ability to initially learn the sigil sequence. The most dangerous here would be a partially hidden sequence that you think you see, but you actually only see parts of. You would have no way of knowing if you learned the full sequence or not. An error in the sigil sequence could lead to dire consequences, depending on your DM's ruling.

• There could be a likelihood of failure based on how well you copied/remembered the sigil sequence, considering you hadn't fully understood the mechanics of the spell at the time you learned the sigil. This could be a DC based on WIS or your spell-casting ability. Failure with this spell could be rather disastrous depending how your DM plays it, and the extent of the failure.

Answer 3

Think of it like this.

Without knowing Chinese, how to read, write or speak it...copy down a page of Chinese text from a recipe book.

Then, years later, having learned Chinese, use that page of text by handing it over to a waiter, and you have to eat whatever he brings you.

Magic results may be worse than that, it's notoriously finicky, and the waiter can be befriended into bringing you actual edible things and not bricks or other atypical Chinese ingredients.