What kind of signs would a baby with autism show?
There were subtle signs with both my DDs but the problem with ASD is that most of the behaviours are also present to a different extent in neurotypical children.
For example, my DD1 was a ridiculously poor sleeper. That was a symptom of her ASD and it was extreme. However, lots of parents say their child is a poor sleeper. It takes a lot of drilling down to establish which cases are extreme.
My DD2 didn't really make eye contact during BFing. I put it down to the fact that BFing turns their head away in comparison to formula feeding. It was a symptom of her ASD but I wouldn't want someone whose baby BFs at such an angle that they can't easily make eye contact to worry.
Part of the problem with the MMR is that it's really common for children with ASD to experience a regression in the months following the age they would usually receive the vaccination. That creates a false link in people's minds and anti-vaxers think it's proof. It isn't and that regression happens in non-vaccinated babies too.
You need to file the vaccine conspiracy theories alongside the flat earthers, the "we never landed on the moon"ers and those who deny the holocaust. Just shrug and move on.
There's no cast iron guarantee that vaccination is going to give the best outcome for your DC because rare vaccination reactions do happen and for a very small number of children, the vaccine doesn't work but the chances of your child coming to harm if you don't vaccinate are hugely increased.
A lot of parenting is about making a judgement based on the information available to you and hoping you got it right. This is no different. Please just base your decision on reputable information from qualified professionals in the field, not conspiracy theorists and people who are looking for excuses not to stick nasty needles in their precious snowflake babies.