input type=number not possible to insert negative numbers on mobile phone

In short, there's no way to make the minus sign show up on Samsung Android numeric inputs. Here are a few workarounds I've run across:

1) Google Keyboard

The user can install a different keyboard (like Google Keyboard). Obviously not ideal to have people install something though.

2) Negate Button

As @Cris already suggested, add a button which will negate the value. If you've got the screen real estate then great.

3) Double Dot Trick

We ended up with a fairly ugly workaround where the user can press . twice and it will negate the number. Totally non-discoverable but an extra button wasn't an option for us.

https://gist.github.com/bendytree/936f6b9b4c0e10138b7e9158b5fd05d9

The issue is specific to Samsung custom keyboard - hooray to vendors who think they're smarter than everyone. Here is another example of this issue at work

Make an extra input field. A "sign" checkbox, selecting natural or negative integers.

Then hook the onchange event of the checkbox so that you update the number view to reflect the chosen sign.