I'm looking into Gronsfeld now, apparently you combine a string of letters with a string of numbers and the numbers move the letters along. (So string FFFFF with code 54321 would produce ABCDE... I think!)
I feel like the numbers in the URL (84552723) look like they could be a decryption key - any ideas of gibberish to run through it? IHTHTB doesn't produce anything (nor would I expect it to now that a TH has disappeared) and it doesn't really make any sense for the string to be shorter than the number, but maybe if I add the "CD" from twitter?
ETA: I just checked the website and couldn't see the Gronsfeld bit under the signature. Invisible text! Good catch!
I wonder if IHTHTB / IHTB is something really simple that's been put through a cipher already, then we need to reverse-engineer the cipher from the signature. Maybe too complicated??
ETA2: Basically with a Gronsfeld cipher each letter has to be within 9 letters of the word. The only word you can make out of IHTB is EAST, which doesn't feel like a lead. IHTHTB can produce EAREST, which is one letter away from DEAREST... but doesn't feel like a lead either.
Maybe the code is TIHTB - with the T in the top right corner of the picture?