There is no evidence of such ship-shore co-ordination in the U-boat logs. It is also highly unlikely that it took place (except perhaps in the imagination of the beach signallers and paranoid US authorities), because by 1918 the German navy's spy network in the US was non-existent (even before that it was largely confined to the activities of Cdr Von Rintelen in 1914 and 1915 and, after his exposure, to the bungling of Germany's 2 top idiots: Capt Boy-Ed and Col Von Papen at the German embassy in Washington - until they were expelled in 1916/17). In any event there would have been no way for German authorities to communicate with such people to advise them of the U-boats' arrivals, due to the lack of physical communication owing to the British blockade, lack of access for potential operatives in the US to cable communications, lack of usable ciphers, and censorship in the US.