What are the connotations of "Avnei Zikaron"?
Rashi: It is so that Hakadosh-Baruch-Hu should see the names of the tribes before Him and remember their righteousness. 1
With the result that Hashem bestows His Mercy upon them (Seforno).
Why is l'Zikaron written Chaser here (without a Vov), and regarding Machatzis ha'Shekel (30:16) it has a Vov?
Moshav Zekenim (30:16): The Avnei Efod are a remembrance only when they are on his shoulders, but [the sockets mads from] Machatzis ha'Shekel are a remembrance as long as they exist.