The definition of treason is a follows (from Dictionary.com):
trea·son
noun
1.
the offense of acting to overthrow one's government or to harm or kill its sovereign.
2.
a violation of allegiance to one's sovereign or to one's state.
3.
the betrayal of a trust or confidence; breach of faith; treachery.
To sign a petition asking to secede from the Union is not only a "violation of allegiance" to our country, it also threatens the security of our country by attempting to divide the country, and thus weaken it. Any move to secede one's state is not an exercise in free speech. It is a betrayal of our country and a direct attack on the federal government and the people it represents. Those who sign such a petition are traitors and should be charged as such.