1)
What are the connotations of "Avnei Zikaron"?
1.
Rashi: Aharon wore the Eifod so that Hakadosh-Baruch-Hu should see the names of the tribes before Him and remember their righteousness. 1
1
With the result that Hashem bestows His Mercy upon them (Seforno).
2)
Why is "le'Zikaron" written Chaser here (without a 'Vav'), whereas in 30:16 regarding the Machatzis ha'Shekel it is written with a 'Vav'?
1.
Moshav Zekenim (in 30:16): Because, whereas the Avnei Efod served as a remembrance only when they were on the Kohen Gadol's shoulders, [the sockets made from] the Machatzis ha'Shekel served as a remembrance as long as they existed.