diff --git a/src/client/signal.ml b/src/client/signal.ml
index ebb3e460..c4c3fa11 100644
--- a/src/client/signal.ml
+++ b/src/client/signal.ml
@@ -5,6 +5,13 @@ module Span = Opentelemetry.Span
 
 let ( let@ ) = ( @@ )
 
+module Proto = Opentelemetry.Proto
+
+type t =
+  | Traces of Proto.Trace.resource_spans list
+  | Metrics of Proto.Metrics.resource_metrics list
+  | Logs of Proto.Logs.resource_logs list
+
 module Encode = struct
   let resource_to_string ~encoder ~ctor ~enc resource =
     let encoder =
@@ -63,8 +70,6 @@ module Decode = struct
 end
 
 module Pp = struct
-  module Proto = Opentelemetry.Proto
-
   let logs = Format.pp_print_list Proto.Logs.pp_resource_logs
 
   let metrics = Format.pp_print_list Proto.Metrics.pp_resource_metrics
diff --git a/src/client/signal.mli b/src/client/signal.mli
index a5c25a27..7c8f7779 100644
--- a/src/client/signal.mli
+++ b/src/client/signal.mli
@@ -1,6 +1,16 @@
 (** Constructing and managing OTel
     {{:https://opentelemetry.io/docs/concepts/signals/} signals} *)
 
+(** The type of signals
+
+    This is not the principle type of signals from the perspective of what gets
+    encoded and sent via protocl buffers, but it is the principle type that
+    collector clients needs to reason about. *)
+type t =
+  | Traces of Opentelemetry_proto.Trace.resource_spans list
+  | Metrics of Opentelemetry_proto.Metrics.resource_metrics list
+  | Logs of Opentelemetry_proto.Logs.resource_logs list
+
 (** Encode signals to protobuf encoded strings, ready to be sent over the wire
 *)
 module Encode : sig