Xindi Emblems and Writing
As we sift through the entire third season of Star Trek Enterprise and look for an emblem representing the Xindi, there is only one candidate that comes into question. It can be seen for the first time in ENT: "The Shipment" and consists of a red triangle with arms that form a kind of triskelion, with an irregularly shaped line drawing in its center, which likely is a Xindi letter. This central symbol is usually surrounded by six boxes with more Xindi letters.
This article identifies the variations of the Xindi emblem on screen and also looks at the Xindi writing and other logos. It appears that pretty much all of the Xindi graphics were auctioned off by It's a Wrap!, so we can show various photos as well.
"The Shipment" introduces the distinctive red Xindi triskelion emblem with a white Xindi letter in the middle. It can be seen as a shoulder patch on the uniforms of the Xindi-Arboreals and in a large size on two glass panes, each of which consists of three parts.
The standalone triskelion logo without the surrounding boxes and Xindi letters appears only in this one episode.
Xindi council emblem
"The Shipment" also shows the version of the Xindi emblem for the first time that would appear repeatedly in later episodes. Inside the lid of a small container we can see a green sticker with the red emblem in the middle. Outside this red central symbol there are six boxes, each with one Xindi character. These boxes are arranged in a ring around the center. This whole emblem apparently symbolizes the Xindi Council, which is composed of presently five species (Arboreals, Primates, Reptilians, Insectoids and Aquatics). Very likely the sixth letter, probably the black one, is meant to represent the now extinct Xindi-Avian species.
This emblem reappears on walls and consoles inside Degra's ship in "Proving Ground". We can see it somewhat better in "Stratagem", "Damage", "E2", "The Council" and "Zero Hour". The emblem never appears in the Xindi Council room though.
Yet one more logo on a display that can be briefly seen for the first time in "The Shipment" consists of several green and white bubbles that look like an atomic core. It is placed in a red ring. There is no clue what it could mean. Maybe it is just a UI symbol, rather than anything of significance in the Xindi culture. The logo will be better visible in some of the later episodes, such as "Proving Ground", "Stratagem", "Azati Prime", "The Council" and "Zero Hour".
Xindi script is seen for the first time in "Anomaly". There are two variations. The first is shown in white and consists of seemingly uninterrupted line drawings that fit into a rectangular space. The frame and the letters on the left of the screen next to Hoshi's face are Osaarian. Later in the episode, we also see more elaborate characters that consist of curved lines as well and are placed in a ring. These usually appear in green when shown on a computer screen.
In "Rajiin" we can briefly spot black Xindi letters, again without an outer ring. The green, round Xindi letters show up again in "Impulse", "Exile" and several more episodes.
Besides many wall elements and panels with white writing on it, "The Shipment" shows green and blue disks for the first time, each with a white Xindi character in a green ring on it. From now on, these disks would be seen in every subsequent appearance of Xindi consoles. In "Carpenter Street", for instance, we can see several consoles with green or blue disks. These reappear as the interior of Degra's ship debuts in "Proving Ground". This episode is also the first one to show elongated stickers with Xindi letters.
Starships of the Xindi-Insectoids as in "Hatchery" and of the Xindi-Reptilians as in "The Council" also have the familiar characters on green and blue disks attached to consoles and displays. The same applies to the Xindi weapon in "Zero Hour". The HD screen caps give away that these are just paper print-outs.
The initiation medal from the future that Archer presents in "Azati Prime" has an engraved Xindi letter.
32nd century Xindi-Insectoid emblem
A 32nd century Xindi-Insectoid emblem can be seen at the voting in DIS: "...But to Connect", among many other symbols. The emblem consists of the simplified central triskelion, with a new symbol in the center. The exact color is conjectural, as all icons on the transparent display are either red or green, depending on the vote.
Encyclopedia IV emblem
In the fourth edition of the Star Trek Encyclopedia there is a Xindi logo that we haven't been able to find in any of the episodes. It can be seen in both the "Symbols" and "Xindi" entries of the book. Overall, it looks like a normal green letter with an irregular ring around it (a bit like on the colored disks) and with an additional blue dot.
Most screen caps from TrekCore.