There are lots of little things to look out for in babies with silent reflux -
They don't like lying flat
Snuffling/sounding as if they have a blocked nose/coughing
Gulping
Little gasps/sharp intakes of breath (often when asleep)
'Face pulling', mostly while asleep, sometimes together with gulping
Their breath can smell metallic/acidic
You don't always get every symptom, but you know your baby best, so you can look out for little things.
Gaviscon can help, but it can make them really constipated! My DD has silent reflux, and the initial relief with Gaviscon was great, however, it was soon replaced with really struggling to poo. If you are formula-feeding, you can get special anti-reflux formula, which we gave her, but alternated with normal one because it also causes constipation. Alternatively, you can just give half the dose of Gaviscon.
Other things you can do are:
Feed little, but more often
Take breaks when feeding
Keep them upright for 30min after each feed
Get a sling/carrier (it was a life-saviour for us, as she would scream hell down when lying in the pram).
It's awful, we had a really rough time with it for a while. Our DD was eventually put in ranitidine, which really helped, but I had to fight for it, the GP was not keen at all... good luck!