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Vim, 42 strokes

:s/[^A-Z0-9]//g
YPVr-i+&lt;DOWN&gt;&lt;LEFT&gt;|&lt;ESC&gt;&lt;C-V&gt;ky$pYjppVr $xrv


Replace &lt;DOWN&gt; with ↓, &lt;LEFT&gt; with ←, &lt;ESC&gt; with esc and &lt;C-V&gt; with CTRL+V.

Here's an animation of this script running (old version which uses a V instead of a v):



Explanation of the script:

:s/[^A-Z0-9]//g                               # Remove all the characters that are not uppercase or numbers using a Regex.
YPVr-                                         # Duplicate the current, and replace all the characters of the upper one with dashes.
     i+&lt;DOWN&gt;&lt;LEFT&gt;|&lt;ESC&gt;                     # Insert a + on the upper line, and a | on the second line.
                         &lt;C-V&gt;ky$p            # Copy the + and | to the end of both lines.
                                  Yjpp        # Copy the upper line to the bottom two times.
                                      Vr $    # Replace the bottom most line with spaces and put the cursor on the last character.
                                          xrv # Remove the last character and replace the second last character with a v.