How can we excel in a position that does not give us the opportunity to be relevant?

This is what made me successful thus far CW2 (Join to see):
1. Take charge of your career as best as you can
2. Look for a variety of assignments. FA, CAV, IN, EN, etc. Signal equipment varies by unit (EPLRS, INC1B, etc.)
3. Volunteer for everything you can! I went Drill Sergeant and never looked back. (You will stand out more if you can perform well out of your comfort zone (MOS).
4. Make sure your evaluations are dress right dress.
5. Ensure your records are in order.
6. Find the nearest Signal SGM/CSM and talk to him/her frankly and to the point. Find multiple contacts and use them and their advice to guide you. (You may even find a new job if your what they or someone they know is looking for)
7. Call/E-mail the Signal branch mercilessly until you get an answer to your assignment needs.

SFC Casper Savang - My suggestion, find a unit that needs assistance, you are an expert in probably several MOS's, train the troops! See if your command will let you volunteer to assist. I am not sure if you are Active or Reserve, but the junior Soldiers want to learn, it would be great bullet point(s) for your NCOER. It will require you taking personal time, but if you want to grow, go for it! I can not image your command would not support. Set up classes, create training material, train the trainers.... The list is endless. Believe me, once you start, you will open doors that you cannot imagine.

Diversify.
This is a golden opportunity to take on some additional duties that help the organization and build your resume and skills for the next level. Physical Security Officer comes to mind.
There are probably volunteer opportunities in the community. If the environment is permissive enough, see what you can do to energize your co-workers to do something positive for your community periodically.
You could always take the time to work on you. Take some online courses. Knock out SSD or some DL courses. You may not be challenged where you are, but you may find a tougher one in your next assignment. Prepare yourself.
Good luck, CW2 (Join to see)!

I would talk to the GS-13 about doing more and getting more involved with the planning side. The position you are in is difficult to say the least because working for a civilian employee is outside of the norm. However, garrison assignments are great because it is where the national level comes together with the operational side. Being a leader is not always about being in a leadership position. Some of the best leaders lead by example even though they are not in a leadership position. I can empathize with the difficult position you are in but there must be a way to turn that disadvantage into an opportunity.

MSG Gomez hit the nail on the head! I was encouraged to seek out what used to be called "an extra-marital affair". (*you'd get court martialed for saying it today I'm sure) It was a way of verbalizing, to hard headed individuals, the concept of getting out if your comfort zone. You MUST demonstrate 2 direly important points in order to excel:
1) Show me what you've done AND DONE WELL that places you above your peers
2)Demonstrate that there is not a position or assignment that you won't take because YOU ARE WILLING TO TAKE ANY CHALLENGE! HOOAH?
RLTW

I would see the Garrison CSM about taking on an additional duty or two that he needs help with to give you something new to learn and add to your NCOER. The GCSM can then help champion your cause

All you can do is your job to the best of your abilities. Also, see if there are any extra duties that you might be able to do for your unit.

Do your best no matter what!

Take on education and prepare for after retirement. If you can call it that anymore. Take advantage of all the freebies like Clep and things like that. Use your downtime to your advantage. Good luck.

I'm in a bit of a similar spot. I just keep an eye/ear open for extra taskers. Work with/mentor the junior troops on things outside your section. Help your Rising 6 (or equivalent orgs) with even simple things like highway cleanups. Participate in your local Top 3 or other orgs (such as Air Force Sergeant's Association in the AF). Organize the annual, etc events. Take on extra duties, particularly the ones no one else typically wants. Take classes, or at least some PME-type CBTs. Teach classes as available at your local PME center, if they offer the opportunities. Talk to those of similar, or even better higher, rank about their experiences and look for ways to improve. Try to find out others who've been in a position you might like to move on to and ask them to coach you on what's needed/how best to execute said job if you can get it. Find some good local charities/orgs and work with them to develop new events/activities to further their goals and get you out in the community.
There are a fair number of ways to make yourself visible so you don't have to be seen as mediocre as your job might be. Sometimes you'll just have to go a bit further than other positions might to find them.

Edit: This is all with the grain of salt that I'm not overly familiar with Garrison spots in other services, but figuring it's similar to my HQ job.