In 2 weeks, my Dad and I are visiting Normandy and taking a 3-day tour of the Landing beaches and inland sites such as Brecourt. My Grandfather was a Sergeant in the Royal Corps of Signals and took part in the invasion, but we do not know anything about his war other than that. That, and that he once told my Dad he "served alongside Americans", so we do not know for sure what beach he landed on, or if this was in combat or in logistics or a technical capacity. We just want to know what kind of thing he may have been doing as we visit the beaches, and where he may have gone afterwards, as the MoD won't get his records back to us on time. Also... I feel that signalmen are often overlooked in the narrative of warfare, so this may shed some light for others too!
That's a little thin to go on but I'll take a stab. A service number might help.
Firstly, you're correct signalmen, and other supporting troops, receive much too little attention. Especially in assault scenarios, such as D-Day, they're out there taking as much fire as any one trying to get their job done without even the 'satisfaction' of getting to shoot back.
Signalers would have been attached to the headquarters of combat units of the army from Army Group (i.e. Montgomery's level) down to at least Brigade level, or anywhere in between and possibly lower. When your grandfather landed would depend immensely on the level he was attached at. Obviously he would almost certainly not have landed as part of the initial 'assault' waves which were almost exclusively combat arms and engineers. However he may have landed as early as an hour or two after the first assault.
The British and Canadians landed at three beaches on the Eastern area of the invasion zone. It's unlikely he landed at the central one of the three beach, Juno, since that was the Canadian zone and they had their own signalers. Though it is possible, I'll skip it.
The far eastern beach, Sword, stretches from Ouistreham to Saint-Aubin-sur-Mer. If your grandfather landed here he would likely have quickly moved to the East to link up with the paratroops who had dropped around Benouville to secure the Eastern flank.
However, IF the "served alongside Americans" quote relates to D-Day and the period immediately after, it's very likely he landed at Gold Beach. Which is the Western most of the British/Canadian sector. Gold beach stretches from Le Hamel to La Rivière. The units here pushed south after landing and also West to link with the Americans landing at Omaha beach a few miles to the West.
What exactly he was doing would, again, depend on what level he was attached to. If he was attached to a lower level unit his might have had a hard cart with equipment etc to bring ashore with his unit. At higher levels he might have been responsible for a large truck mounted radio set. Remember that the Corps of Signals have a large range of responsibilities which ranged from actually sending and receiving radio messages to maintaining the equipment including wired telephones and even the wires themselves.
TL;DR Your grandfather almost certainly landed at either Gold or Juno beach and then moved West or East respectively.
(Incidentally my grandfather was also in the Royal Signal Corps, but he landed in North Africa during Torch and then made his way up Italy. He was attached to a fairly high level HQ so he got to drive most of the way.)