You can telegraph caring and love for someone with dementia with a simple hug. Communication with body language -- especially touch -- is easily understood even as other language skills (like interpreting the meaning of words or following a conversation) become more difficult. And touch is reassuring when so much feels uncertain.
Believe it or not, there's a best way to hug someone with dementia:
Ideally, approach from the front so the person has a visual cue. Approaching from behind or beginning to hug before your face is seen can be frightening.
Make sure your hug is of sufficient length -- seven seconds is a good rule of thumb. That's long enough that your loved one really gets the message of your intention. A perfunctory hug can be too quick to register.