You can write Mr. al-Humsi and offer words of encouragement by sending a letter or postcard to:

Mamun al-Humsi
c/o Director
'Adra Prison
Ministry of Interior
Merjeh Circle
Damascus
Syrian Arab Republic

Mr. al-Humsi speaks both Arabic and French, a French phrase to use is:

Ne sois pas découragé.

Tu n’es pas oublié.

 
It translates to: 
Do not be discouraged.  You are not forgotten.