Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

Yes, it is.

Showing solidarity with people who are wrongly imprisoned is something honorable. It falls under a Muslim showing support to his Muslim brothers and sisters. The Prophet (peace be upon him) said: “the example of Muslims toward each other in love, mercy and care is like the example of a body. When one part feels pain it echoes to other parts of the body.” (Muslim)