I have had this problem, I called three as i was panicking from other replies regarding battery etc. And its nothing to worry about. It is to do with how the view is set up for notications. Go to Settings....Notification Panal......Reset (next to active) and then resart your phone. Bye Bye arrows and phone is fine.

Thanks for your tip which seems to have worked. I only updated yesterday and it meant I couldn't send sms messages at all yesterday afternoon. Frustrating that there is no proper info anywhere.

Been having the same issues as you guys. Also UK based here and completely unable to send sms unless I restarted the phone every time. I believe the arrows are to do with Voice over LTE and think I found a solution (the arrows haven't come back since I rebooted my phone after doing this)...
Go to your settings, use the magnifying glass to search and type More Networks. Go into this and then into Mobile Networks. I think what displays here could be different depending on your carrier or country. Some may have a VOLTE option. For me I went into Network mode and had 3 options....
LTE/WCDMA/GSM (auto connect)
WCDMA/GSM (auto connect)
WCDMA only
Mine was set to the top one so I've changed to the middle. All seems to be working ok at the moment!

Credit where it's due. I found this info on the site below regarding turning VOLTE on but just used the guide to get me to the right place to turn it off.
http://www.sebertech.com/2014/09/turn-volte-call-and-use-advanced.html?m=1

Same problem here, s5. Some samsung apps updates about 8 hours ago when I switched to wifi and since then I've seen this symbol in the top bar and haven't been able to send sms messages.

I'm the same as you Renny and it is massively frustrating!

Like everyone else, I hadn't seen this symbol until the latest update. I'm in the UK and my network doesn't support 4G in my area. But when this symbol is displayed SMS doesn't work. Rebooting seems to solve the problem for a while, but it keeps coming back.

Ever since the update my phone has been awful. But I changed the network mode from LTE/WCDMA/GSM to WCDMA/GSM and this got rid of the arrows. So I presume it's some thing to do with 4G.I then changed the networked mode back and tried turning off VoLTE but the arrows stayed, so I really don't know :/

I believe it's VoLTE icon. Which carrier are you guys with?

Has anyone come up with a solution or even come up with an explanation to what it is

Appeared on my S5 after a software update the other day. Not discovered what they mean yet.

Me too. Software upgrade this morning and it's been there since. I can't find any info telling what it is anywhere

I got the same after an update and can't find the answer anywhere. Some have suggested it's lte but i don't think it is. Annoying that this isn't explained

Sorry don't know either, but wondering the exact same thing. Software update this morning and this notification appeared!

Arrows appeared on mine to. Worried this is using valuable data .

Same problem after update this morning now I'm having screen rotation problems.

I don't know. I'm wondering the same thing.can't find the answer nowhere

What are the 2 horizontal white arrows. On my galaxy s5 notification bar. And how do I get them off