[u]Marks[/u]: You need a lot of Armor with Nami, since she is squishy and doesn't deal a lot of damage overall. Since the patch you build a lot of ap so u will eventually deal damage, though i don't think it is worth it for the laning phase to give up the armor for damage u might deal later. What might be to consider is hybrid pen marks, since then your e does deal damage you can actually notice when you use it on yourself
[u]Seals[/u]: You [u]REALLY need[/u] Armor, other runes to consider would be the 0.25 Gold/ 10 sec, though if u calculate it, its about 540 gold in a 40 minute game, armor seals are about worth of a cloth armor, which costs 300, therefore its use starts around 23 minutes, and to consider that u really need to be able to win your lane with your adc and not earn additional 13,5 gold each minute, i think u should really go for the philosophers stone since u need mana and health regen anyways.
[u]Glyphs[/u]: well since new season ap scales with utility, therefore the more ap the more movement speed with your passive, awesome in team fights for your team to reposition after your ulty if you hit a nice w that bounces off of most of your allies
[u]Quints[/u]: Since the patch i don't find it really hard to earn enough gold as support, u get quite the amount of assists and if you work your support item correctly gold quints are unneccesary. Go for AP instead!