I'm on Humira too, although I haven't flow with it yet. I have flown, including in the U.S., with MTX syringes. I just put them in the clear plastic bag with other toiletries. Security never commented on it at all. I wouldn't worry too much about it; many people travel with insulin, for example.
The TSA's own web site (http://www.tsa.gov/travelers/airtravel/specialneeds/editorial_1374.shtm) says
********** QUOTE starts HERE ************
All medications in any form or type (for instance, pills, injectables, or homeopathic) and associated supplies (syringes, Sharps disposal container, pre-loaded syringes, jet injectors, pens, infusers, etc.) are allowed through the security checkpoint once they have been screened. Atropens, an auto-injection system that can help treat many emergency conditions (low heart rate, breathing problems, and excess saliva related to insecticide, nerve gas or mushroom poisoning) are also allowed.
We recommend, but do not require, that your medications be labeled to assist with the screening process.
************ End Quote
If you're really worried, you could print the page from the web site and keep it with you.
Safe travels, and good luck with the Humira.
Healing well with psoriasis, PsA, and hypogonadism, and happy to share my experiences.