The last episode of the second and final season of this science fiction series features proeminently in its last scene a large flag, being hoisted by huddling transhuman/transgenics under siege on top of an abandoned building. This episode, "Dark Angel" series #221, intitled "Freak Nation", was 1st aired on 5 March 2002 on Fox Television. You can see the flag on this screencap and this one.

This flag is a ~2:3 WRN horizontal triband with a large white dove over all and a patch of red barcode on the black stripe. The barcode on black stands for the Manticore millitary complex/company "X5" breed of "transhuman/transgenics" (which had an ID barcode on thir necks), hiding in the dark; the red stripe stands for their "present" situation, chased by their former "owners" and hated by the ignorant masses; the white stripe stands for the light, where "transhuman/transgenics" want to live free.

The flag is presented as identitary symbol, akin to other US ethnical "heritage" or lifestyle "pride" flags. It was created by Joshua, a lionine "transhuman/transgenic". Here's the relevant transcription, taken from www.darkangelfan.com :

Max walks over to Joshua, who is painting a flag. It has a black stripe on the bottom, a red stripe in the middle, and a white stripe on top. In the middle of the black stripe, there is a barcode. In the middle of the flag, Joshua has painted a white dove, wings spread.)

MAX: Hey, Joshua.

JOSHUA: Hey.

MAX: Whatcha doin'?

JOSHUA: It's a flag. It's our flag.

LUKE: Yeah, 'cause we're gonna need a flag when our transhuman drill team is marching down Fifth Avenue in the St. Paddy's Day Parade.

DIX: Let's not forget halftime at those Seahawks games.

MAX: Hey, cut it out.

(Joshua explains the flag. He begins by pointing to the barcode.)

JOSHUA: This is you, me, even them. It's all of us. (Points to the black stripe) This is where we came from — where they tried to keep us.

MAX: In the dark.

JOSHUA: Secret. (Points to the red stripe) This is where we are now, because our blood is being spilled. (Points to the white stripe) This is where we want to go.

MAX: Into the light.

JOSHUA: Right.

António Martins-Tuválkin, 19 February 2005

It should be noted the flag is only seen in the episode from what might be considered the "reverse hoist." I seem to recollect that the filming for this part of the episode was abbreviated somewhat because it was filmed on a day that there was rain on site in Vancouver and the flag, being painted, began to run.

Regarding the barcode, it was used by all of the generations of the transgenics (including the X6's which play a large role in the last season), except for the few prototypes, of which Joshua was one.

And I believe that one can barely see the barcode extending under the dove's right wing.
Phil Nelson, 19 February 2005

Yet the barcode is clearly described as being part of the flag in the "flag design scene":

(Joshua explains the flag. He begins by pointing to the barcode.)

JOSHUA: This is you, me, even them. It's all of us.

When I first saw this flag I thought the red stripes were blood drip trails. (Red on black barcode is not a good idea — just like the idea of barcode on skin.)
António Martins-Tuválkin, 20 February 2005

I think that the barcode extends farther to the left — from underneath the tail on the right to halfway along the bottom of the wing in the other direction. The gif only has it going about 2/3 as far.

Also, I think the dove may be a bit too small — compare the distance between the tail and the bottom of the flag, or between the right wingtip and the top.
Eugene Ipavec, 20 February 2005