This is a question I hear a lot during my animal communication sesions with companions that have crossed over. My human clients think they see something or suddenly are in possession of something that reminds them of their companion, and they wonder "is this a sign?". The quick answer is "YES".
When you think of everything as a form of energy, then you understand that energy does not die. It simply changes form. That means that while your beloved companion is not physically present, they are still with you. I don't mean "with you" as in memories. I mean they are with you in the space you take up. Here is a great analogy I read in "Whispers of Love" by Gina Simone. In the book, she describes Source or Life as the ocean. If you dip two different types of cups into the ocean to fill them, the water in each cup is still part of the ocean, it is just in a different vessel. When you pour that water back into the ocean, it becomes one again with the the greater Source.
So, we are the vessels, the cups. Our bodies, no matter what shape, color, size, or being are all part of the ONE. Because of this, we are all, always connected. (It also shows how silly it is to be racist or sexist or discriminatory towards anyone who looks different than you). Being connected, does not end when life leaves the body. It simply changes form. What remains connected is our souls.
So what signs are real and what aren't? I suppose that is up to you and your level of belief. I do not believe in coincidences. To me, those are signs. If you are missing your friend and go for a drive and turn the radio on and a song that was special to you and your friend comes on....that is a sign. Looking for a home and you read the notes on zillow and it mentions a phrase that holds ogher meaning to you...that is a sign. Seeing a specific bird outside your window....that is a sign. Now don't get me wrong. Birds are around us all the time. Music plays on the radio all the time. We don't hold a monopoly on phrases. What makes these things a sign is the timing. You looked outside your window at the exact moment the bird came into view long enough to be seen. You flipped on the radio at the exact moment the dj decided to play your song. The phrase you hold dear was purposely used by that realtor/homeowner and you scrolled their ads at that time.
Sometimes signs are not obvious or physical things. You may have a sudden chill or smell something no one else does; signs can also come in dreams, playing out scenarios in your mind to help you remember something. Sometimes, we see shadows crossing the room. These are all real. You are not crazy.
Animals understand the continuum of the soul. Did you every see your companion sitting nicely looking at something as if someone was speaking to them? They are listening to a soul. I remember many years ago, I had a beautiful Springer Spaniel named Athena. We lived in the Bronx at the time. The apartment we moved into came up suddenly and I was so thrilled to be able to get it. I painted and decorated and really loved the apartment. The only weird thing was that I would sometimes smell "old lady" perfume. One day, I was walking from the bedroom to the kitchen when I glanced over to Athena and saw her sitting down nicely with her head tilted up and the hairs on the top of her head were moving. I froze in place because when I pet her head, that is exactly her position and her hair moved in the same exact way. I called her name and I smelled that perfume. Athena turned to look at me but did not move until i visibly saw her head patted- in that "ok! good girl" type of way. I was a little freaked out at the time, but Athena was calm as could be. As it turned out, the tenant in the aparmtnet before me, was a little old lady who had passed away. Everyone in the building said she was a lovely woman. I spoke to her and told her she was welcome to visit Athena but not to do anything creepy. lol We lived there for several years, happily.
Whatever it is, if you think something is a sign, it is. If you think "what a coincidence", it is a sign. Our loved ones that passed visit us to give us messages and comfort. They keep us company and guide us ( or try to. Sometimes we just don't listen). They also send signs to remind us of something: a memory, a person, or simply to live joyfully. No one from the other side wants us to be sad and gloomy and crying. If you want to honor them, live joyfully. Be happy. Be kind.