The letters of the Mayan alphabet do not really exist as such in fact from the translation that Diego de Landa did.
According to the story Diego de Landa had two translators to whom he asked them to translate the alphabet. He mentioned the letter to them and the translators drew the glyph.
When Diego de Landa wanted to translate the Mayan documents as stelae or codices, he realized that none of the drawings matched, so he assumed that the translators lied to him.
There is a book called r"Relations of things of Yucatan" in which there is a page that has the original drawings of the translation by Diego de Landa.