Remember, if you haven't used our clues pages yet, check out the instructions here to learn how they work and how to best utilize them.
These are some very specific shapes.
In fact, if you put these all together they seem reminiscent of a different shape...
...back on the first postcard.
Final Solution: Using the large symbol on the front of the very first postcard you can assign a symbol to each of these shapes. Using the guide on the back of this postcard you can assign a letter to each of those symbols. Taken all together, you can extract the plaintext: "Anaconda."
How am I supposed to line up all these letters?
If only you had a map of some kind...
If it helps, you've already connected this card to another card.
Final Solution: Using the lines from the first card with the shape on the front, you can trace a path that leads from letter to letter. When extracted, you'll get the plaintext: "Send me the confirmation number."
Have you solved the other stamps?
Final Solution: The numbers translate to the word "Tannin."