Nabataean letter has evolved through their history, it had
different shapes depending on the time and place it was written,
some letters had different ways of writing depending on the
place in the word, they did not put space between words so
the letters written differently show it is the end of the
word, a word could start on a line and continue on the next
without having any sign, later writing had some letters joined,
and that was the time when Arabs took the Nabataean alphabet
and with some adaptation they started using it for writing
in their own language, Arabic had more letters, so they had
to add some signs to some letters so as to make a bigger collection.
The letters below are from the inscriptions
in Petra that date to the first century a.d., for more information
about ancient Nabataean Writing, a good book in Arabic is
"The Nabataean civilization through their inscriptions"
by Dr. Ahmad al Ajluni.