Try this:
`/setblock ~ ~1 ~ wall_sign 5 [replace|destroy|(none)] {Text1:"{\"text\":\"Your Text Here\"}"}` << never forget to use backslashes before an opening or closing quotation.

If you want it to have colors:
`/setblock ~ ~1 ~ wall_sign 5 {Text1:"{\"text\":\"Your Text Here\",\"color\":\"your_color\"}"}` << on using colors, for spacing (such as red or dark red), use an underscore to indicate it as space ; see colors here: http://minecraft.tools/en/color-code.php , use the color names; never forget to use backslashes before an opening or closing quotations, right :) .

For text styles:
`/setblock ~ ~1 ~ wall_sign 5 {Text1:"{\"text\":\"Your Text Here\",\"color\":\"your_color\",\"bold\":\"true\"}"}` << existing style tags: bold, italic, underline, obfuscated (or randomizing text) only use boolean responses on these tags (like true or false. 0 or 1 is not accepted.);

To put text on appropriate text line:
For 1st line: Text1 tag;
For 2nd line: Text2 tag;
For 3rd line: Text3 tag;
For 4th line: Text4 tag;
(take note that these Text~ tags have same tags inside, like the colors and style tags); (also take note that signs only have 4 lines :) .)

Want all lines to be put? Use them altogether.